SubmittingPatches: update GMail section
Even if you use imap-send to throw your drafts in the outbox, using their
web interface will mangle your patches. Clarify that the imap-send is
meant to be used together with a real MUA that can use IMAP drafts, and
remove instructions related to the web interface, which is irrelevant.
Add description of send-email as an alternative.
Use --cover-letter, and do not use -C nor --no-color, on the example
command line for format-patch.
Signed-off-by: Junio C Hamano <gitster@pobox.com>