examples: console: add a readme with an overview of examples

examples/system/console/README.md

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+# Console examples
+
+(See the README.md file in the upper level 'examples' directory for more information about examples.)
+
+Examples in this directory illustrate the usage of the [Console Component](https://docs.espressif.com/projects/esp-idf/en/stable/api-guides/console.html#console) to create an interactive shell on the ESP chip.
+
+## basic example
+
+This example illustrates high-level Read-Eval-Print Loop API (`esp_console_repl`).
+
+This example can be used with UART, USB_OTG or USB_SERIAL_JTAG peripherals. It works on all ESP chips.
+
+It is the recommended starting point when getting familiar with console component.
+
+## advanced example
+
+This example illustrates lower-level APIs for line editing and autocompletion (`linenoise`), argument parsing (`argparse3`) and command registration (`esp_console`). 
+
+These APIs allow for a lot of flexibility when building a console application, but require more code to be written.
+
+While these APIs allow for a console to be implemented over various interfaces (UART, USB, TCP), this example works with UART only.
+
+## advanced_usb_cdc example
+
+This example is similar to the one above, except it works over USB CDC provided by USB_OTG peripheral.
+
+Currently it can be used on ESP32-S2.