EDK II Contributions.txt: Update patch format information

Update to show what the patch looks like in email form.

NOTE: This does not modify the wording of the "TianoCore Contribution
      Agreement 1.0" section

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16297 6f19259b-4bc3-4df7-8a09-765794883524