[CK] updated github repo link
The location of the github repo has changed; the landing page of the
docs needs to reflect this.
Updated only the git repo links in the docs folder.
Also added info to the install doc about how to do a sparse checkout.
Updated some refs that were messed up while I was at it.
* creation of install doc and refactor of doc in general
* updates based on review comments
* updated based on review comments
* updated readme and contributors markdown
* added extra note to not use -j on its own
* added note about smoke tests and regression tests
* made changes as per Illia's feedback
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Co-authored-by: Aviral Goel <aviral.goel@amd.com>