mailmap doc: create a new "gitmailmap(5)" man page

Create a gitmailmap(5) page similar to how .gitmodules and .gitignore
have their own pages at gitmodules(5) and gitignore(5). Now instead of
"check-mailmap", "blame" and "shortlog" documentation including the
description of the format we link to one canonical place.

This makes things easier for readers, since in our manpage or
web-based[1] output it's not clear that the "MAPPING AUTHORS" sections
aren't subtly different, as opposed to just included.

1. https://git-scm.com/docs/git-check-mailmap

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 33 insertions, 0 deletions

diff --git a/Documentation/mailmap.txt b/Documentation/gitmailmap.txt
index 4a8c276529..8b07f9c5d7 100644
--- a/Documentation/mailmap.txt
+++ b/Documentation/gitmailmap.txt
@@ -1,9 +1,28 @@
+gitmailmap(5)
+=============
+
+NAME
+----
+gitmailmap - Map author/committer names and/or E-Mail addresses
+
+SYNOPSIS
+--------
+$GIT_WORK_DIR/.mailmap
+
+
+DESCRIPTION
+-----------
+
 If the file `.mailmap` exists at the toplevel of the repository, or at
 the location pointed to by the mailmap.file or mailmap.blob
 configuration options, it
 is used to map author and committer names and email addresses to
 canonical real names and email addresses.
 
+
+SYNTAX
+------
+
 In the simple form, each line in the file consists of the canonical
 real name of an author, whitespace, and an email address used in the
 commit (enclosed by '<' and '>') to map to the name. For example:
@@ -27,6 +46,10 @@ commit matching the specified commit email address, and:
 which allows mailmap to replace both the name and the email of a
 commit matching both the specified commit name and email address.
 
+
+EXAMPLES
+--------
+
 Example 1: Your history contains commits by two authors, Jane
 and Joe, whose names appear in the repository under several forms:
 
@@ -73,3 +96,13 @@ Santa Claus <santa.claus@northpole.xx> <me@company.xx>
 
 Use hash '#' for comments that are either on their own line, or after
 the email address.
+
+
+SEE ALSO
+--------
+linkgit:git-check-mailmap[1]
+
+
+GIT
+---
+Part of the linkgit:git[1] suite