doc/send-email: mention handling of "reply-to" with --compose
The documentation for git-send-email lists the headers handled specially
by --compose in a way that implies that this is the complete set of
headers that are special. But one more was added by
d11c943c78
(send-email: support separate Reply-To address, 2018-03-04) and never
documented.
Let's add it, and reword the documentation slightly to avoid having to
specify the list of headers twice (as it is growing and will continue to
do so as we add new features).
If you read the code, you may notice that we also handle MIME-Version
specially, in that we'll avoid over-writing user-provided MIME headers.
I don't think this is worth mentioning, as it's what you'd expect to
happen (as opposed to the other headers, which are picked up to be used
in later emails). And certainly this feature existed when the
documentation was expanded in
01d3861217 (git-send-email.txt: describe
--compose better, 2009-03-16), and we chose not to mention it then.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>