send-email: document --mailmap and associated configuration

241499a ("send-email: add mailmap support via sendemail.mailmap and
--mailmap", 2024-08-27) added support for --mailmap, and the associated
sendemail.mailmap.* configuration variables. Add documentation to
reflect this feature.

Fixes: 241499a ("send-email: add mailmap support via sendemail.mailmap and --mailmap")
Signed-off-by: Jacob Keller <jacob.keller@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: jacob-keller

Documentation/config/sendemail.txt

@@ -30,6 +30,21 @@ sendemail.confirm::
 	in the linkgit:git-send-email[1] documentation for the meaning of these
 	values.
 
+sendemail.mailmap::
+	If true, makes linkgit:git-send-email[1] assume `--mailmap`,
+	otherwise assume `--no-mailmap`. False by default.
+
+sendemail.mailmap.file::
+	The location of a linkgit:git-send-email[1] specific augmenting
+	mailmap file. The default mailmap and `mailmap.file` are loaded
+	first. Thus, entries in this file take precedence over entries in
+	the default mailmap locations. See linkgit:gitmailmap[5].
+
+sendemail.mailmap.blob::
+	Like `sendemail.mailmap.file`, but consider the value as a reference
+	to a blob in the repository. Entries in `sendemail.mailmap.file`
+	take precedence over entries here. See linkgit:gitmailmap[5].
+
 sendemail.aliasesFile::
 	To avoid typing long email addresses, point this to one or more
 	email aliases files.  You must also supply `sendemail.aliasFileType`.

Documentation/git-send-email.txt

@@ -414,6 +414,12 @@ exists when 'git send-email' is asked to add it (especially note that
 Failure to do so may not produce the expected result in the
 recipient's MUA.
 
+--[no-]mailmap::
+	Use the mailmap file (see linkgit:gitmailmap[5]) to map all
+	addresses to their canonical real name and email address. Additional
+	mailmap data specific to git-send-email may be provided using the
+	`sendemail.mailmap.file` or `sendemail.mailmap.blob` configuration
+	values. Defaults to `sendemail.mailmap`.
 
 Administering
 ~~~~~~~~~~~~~