Document that the meaning of a Signed-off-by trailer can vary from
project to project in the end-user documentation, and clarify what
it means to this project.
* bk/sob-dco:
Documentation: stylistically normalize references to Signed-off-by:
SubmittingPatches: clarify DCO is our --signoff rule
Documentation: clarify and expand description of --signoff
doc: preparatory clean-up of description on the sign-off option