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, 108 insertions, 0 deletions

diff --git a/Documentation/gitmailmap.txt b/Documentation/gitmailmap.txt
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index 0000000..8b07f9c
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+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:
+--
+	Proper Name <commit@email.xx>
+--
+
+The more complex forms are:
+--
+	<proper@email.xx> <commit@email.xx>
+--
+which allows mailmap to replace only the email part of a commit, and:
+--
+	Proper Name <proper@email.xx> <commit@email.xx>
+--
+which allows mailmap to replace both the name and the email of a
+commit matching the specified commit email address, and:
+--
+	Proper Name <proper@email.xx> Commit Name <commit@email.xx>
+--
+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:
+
+------------
+Joe Developer <joe@example.com>
+Joe R. Developer <joe@example.com>
+Jane Doe <jane@example.com>
+Jane Doe <jane@laptop.(none)>
+Jane D. <jane@desktop.(none)>
+------------
+
+Now suppose that Joe wants his middle name initial used, and Jane
+prefers her family name fully spelled out. A proper `.mailmap` file
+would look like:
+
+------------
+Jane Doe         <jane@desktop.(none)>
+Joe R. Developer <joe@example.com>
+------------
+
+Note how there is no need for an entry for `<jane@laptop.(none)>`, because the
+real name of that author is already correct.
+
+Example 2: Your repository contains commits from the following
+authors:
+
+------------
+nick1 <bugs@company.xx>
+nick2 <bugs@company.xx>
+nick2 <nick2@company.xx>
+santa <me@company.xx>
+claus <me@company.xx>
+CTO <cto@coompany.xx>
+------------
+
+Then you might want a `.mailmap` file that looks like:
+------------
+<cto@company.xx>                       <cto@coompany.xx>
+Some Dude <some@dude.xx>         nick1 <bugs@company.xx>
+Other Author <other@author.xx>   nick2 <bugs@company.xx>
+Other Author <other@author.xx>         <nick2@company.xx>
+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