doc: Edit the Application Contribution section.

Based on Carol's original contribution. Edited based
on comments made to the original change.
Added better labels and links to other places in
the docs.

Change-Id: Iaff7d1849d7ab7c8276ac9fca87070442ce956fd
Signed-off-by: L.S. Cook <leonax.cook@intel.com>
Signed-off-by: Rodrigo Caballero <rodrigo.caballero.abraham@intel.com>