Rename all the files which will be edited substantially in the next commit, without changing their
contents
Docs will not build for this ocmmit.
This is done so that git doesn't decide we renamed xxx-cmake -> xxx-legacy in the next commit, which
is what it will infer otherwise (and makes rebasing more of a pain than it should be)
1. Moved get-started files, 7 documents in total, from get-started-cmake folder to hw-reference folder;
2. Deleted get-started files, 7 documents in total, in get-started folder;
3. Updated links in get-started-cmake/index.rst and in get-started/index.rst;
4. Modified descriptions for build system in these files.
