Searching for `git send-email' took you to the end of `Submitting Patches'
section which said
You may use your email client or the ‘git send-email’ command.
without further warning or remark.
* doc/contributing.texi (Sending a Patch Series): Move information about
debbugs bug 15361 to subsection. Add git-send-email index entries.
(Submitting Patches): Reference it.