doc: Friendlier advice for contributing to project.

Edited file to have a friendlier tone regarding collaboration standards for the project.

Signed-off-by: Leona Cook <leonax.cook@intel.com>
Change-Id: I5e02b9d9065c3c9c4d96ed67215770167b9b94e1
Signed-off-by: Rodrigo Caballero <rodrigo.caballero.abraham@intel.com>