docs: add linux getting started guide

Currently this is mostly a verbatim copy of macOS guide with some obvious changes.
Exact lists of dependencies for Debian and Arch need to be specified.
Also made minor fixes to Windows and macOS guides:
- changed http urls to https
- added --prefix=$PWD to crosstool-NG's configure
- added chmod u+w for the build output directory

In general, except for prerequisites, Linux and macOS guides are virtually identical.
It might make sense to refactor this into single document with prerequisites being
described in separate docs.

docs/linux-setup.rst

@@ -0,0 +1,156 @@
+Step 0: Prerequisites
+=====================
+
+Install some packages
+---------------------
+
+To compile with ESP-IDF you need to get the following packages:
+
+- Ubuntu::
+    
+    sudo apt-get install git wget make libncurses-dev flex bison gperf python python-serial 
+
+- Debian::
+
+    TODO
+
+- Arch::
+    
+    TODO
+
+
+Step 1: Download binary toolchain for the ESP32
+==================================================
+
+ESP32 toolchain for Linux is available for download from Espressif website:
+
+- for 64-bit Linux::
+
+    https://dl.espressif.com/dl/xtensa-esp32-elf-linux64-1.22.0-59.tar.gz
+
+- for 32-bit Linux::
+
+    https://dl.espressif.com/dl/xtensa-esp32-elf-linux32-1.22.0-59.tar.gz
+
+Download this file, then extract it to the location you prefer, for example::
+
+    mkdir -p ~/esp
+    cd ~/esp
+    tar -xzf ~/Downloads/xtensa-esp32-elf-linux64-1.22.0-59.tar.gz
+
+The toolchain will be extracted into ``~/esp/xtensa-esp32-elf/`` directory.
+
+To use it, you will need to update your ``PATH`` environment variable in ``~/.bash_profile`` file. To make ``xtensa-esp32-elf`` available for all terminal sessions, add the following line to your ``~/.bash_profile`` file::
+
+    export PATH=$PATH:$HOME/esp/xtensa-esp32-elf/bin
+
+Alternatively, you may create an alias for the above command. This way you can get the toolchain only when you need it. To do this, add different line to your ``~/.bash_profile`` file::
+
+    alias get_esp32="export PATH=$PATH:$HOME/esp/xtensa-esp32-elf/bin"
+
+Then when you need the toolchain you can type ``get_esp32`` on the command line and the toolchain will be added to your ``PATH``.
+
+Alternative Step 1: Compile the toolchain from source using crosstool-NG
+========================================================================
+
+Instead of downloading binary toolchain from Espressif website (Step 1 above) you may build the toolchain yourself. 
+
+If you can't think of a reason why you need to build it yourself, then probably it's better to stick with the binary version. However, here are some of the reasons why you might want to compile it from source:
+
+- if you want to customize toolchain build configuration
+
+- if you want to hack gcc or newlib or libstdc++
+
+- if you are curious and/or have time to spare
+
+- if you don't trust binaries downloaded from the Internet
+
+In any case, here are the steps to compile the toolchain yourself.
+
+- Install dependencies:
+
+  - Ubuntu::
+
+        sudo apt-get install gawk gperf grep gettext ncurses python python-dev automake bison flex texinfo help2man libtool
+
+  - Debian::
+
+        TODO
+
+  - Arch::
+
+        TODO
+
+Download ``crosstool-NG`` and build it::
+
+    cd ~/esp
+    git clone -b xtensa-1.22.x https://github.com/espressif/crosstool-NG.git
+    cd crosstool-NG
+    ./bootstrap && ./configure --prefix=$PWD && make install
+
+Build the toolchain::
+
+    ./ct-ng xtensa-esp32-elf
+    ./ct-ng build
+    chmod -R u+w builds/xtensa-esp32-elf
+
+Toolchain will be built in ``~/esp/crosstool-NG/builds/xtensa-esp32-elf``. Follow instructions given in the previous section to add the toolchain to your ``PATH``.
+
+Step 2: Getting ESP-IDF from github
+===================================
+
+Open Terminal.app, navigate to the directory you want to clone ESP-IDF and clone it using ``git clone`` command::
+
+    cd ~/esp
+    git clone --recursive https://github.com/espressif/esp-idf.git
+
+
+ESP-IDF will be downloaded into ``~/esp/esp-idf``. 
+
+Note the ``--recursive`` option! If you have already cloned ESP-IDF without this option, run another command to get all the submodules::
+
+    cd ~/esp/esp-idf
+    git submodule update --init
+
+
+Step 3: Starting a project
+==========================
+
+ESP-IDF by itself does not build a binary to run on the ESP32. The binary "app" comes from a project in a different directory. Multiple projects can share the same ESP-IDF directory.
+
+The easiest way to start a project is to download the template project from GitHub::
+
+    cd ~/esp
+    git clone https://github.com/espressif/esp-idf-template.git myapp
+
+This will download ``esp-idf-template`` project into ``~/esp/myapp`` directory.
+
+
+Step 4: Building and flashing the application
+=============================================
+
+In Terminal.app, go to the application directory which was obtained on the previous step::
+
+    cd ~/esp/myapp
+
+Type a command like this to set the path to ESP-IDF directory:: 
+
+    export IDF_PATH=~/esp/esp-idf
+
+At this point you may configure the serial port to be used for uploading. Run::
+
+    make menuconfig
+
+Then navigate to "Serial flasher config" submenu and change value of "Default serial port" to match the serial port you will use. Also take a moment to explore other options which are configurable in ``menuconfig``.
+
+Now you can build and flash the application. Run::
+
+    make flash
+
+This will compile the application and all the ESP-IDF components, generate bootloader, partition table, and application binaries, and flash these binaries to your development board.
+
+Further reading
+===============
+
+If you'd like to use the Eclipse IDE instead of running ``make``, check out the Eclipse setup guide in this directory.
+

docs/macos-setup.rst

@@ -83,12 +83,13 @@ Download ``crosstool-NG`` and build it::
     cd ~/esp
     git clone -b xtensa-1.22.x https://github.com/espressif/crosstool-NG.git
     cd crosstool-NG
-    ./bootstrap && ./configure && make install
+    ./bootstrap && ./configure --prefix=$PWD && make install
 
 Build the toolchain::
 
     ./ct-ng xtensa-esp32-elf
     ./ct-ng build
+    chmod -R u+w builds/xtensa-esp32-elf
 
 Toolchain will be built in ``~/esp/crosstool-NG/builds/xtensa-esp32-elf``. Follow instructions given in the previous section to add the toolchain to your ``PATH``.
 

docs/windows-setup.rst

@@ -6,7 +6,7 @@ Windows doesn't have a built-in "make" environment, so as well as installing the
 
 The quick setup is to download the Windows all-in-one toolchain & MSYS zip file from dl.espressif.com:
 
-http://dl.espressif.com/dl/esp32_win32_msys2_environment_and_toolchain-20160816.zip
+https://dl.espressif.com/dl/esp32_win32_msys2_environment_and_toolchain-20160816.zip
 
 Unzip the zip file to C:\ and it will create an "msys32" directory with a pre-prepared environment.
 
@@ -35,7 +35,7 @@ Another Alternative Step 1: Just download a toolchain
 
 If you already have an MSYS2 install or want to do things differently, you can download just the toolchain here:
 
-http://dl.espressif.com/dl/xtensa-esp32-elf-win32-1.22.0-59.zip
+https://dl.espressif.com/dl/xtensa-esp32-elf-win32-1.22.0-59.zip
 
 If you followed one of the above options for Step 1, you won't need this download.