add LIBS_FROM_GIT to docs

Also reformat common configuration variables to have an additional
header level which makes it easy to direct link to specific
configuration vars when directing someone.

Reformat header markup to us a more standard == = - for h1, h2, h3

Change-Id: I10bac5a93529cdfbcde0a05f9ebdbc1799d403cd
Merge "add LIBS_FROM_GIT to docs"