Force add submodules.

"git submodule add" is failing complaining about some submodules
being present in .gitignore (I've verified this is not the case) so
to workaround this error, just force add the submodule.

Tested:
Pushed a project to github.

Change-Id: Icbeaf3b933a73f121f6b6f679fd85346fdb9d89f
Added note about downloading source and dependencies.

Also, changed the layout of discussion groups paragraph.

Tested:
Build the HTML docs and verified formatting looks ok.

Change-Id: If97f74c879a345af926a2cdb3f190b376bfb2908