merge(third_party/git): Merge squashed git subtree at v2.23.0

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third_party/git/contrib/hooks/multimail/doc/gerrit.rst

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+Setting up git-multimail on Gerrit
+==================================
+
+Gerrit has its own email-sending system, but you may prefer using
+``git-multimail`` instead. It supports Gerrit natively as a Gerrit
+``ref-updated`` hook (Warning: `Gerrit hooks
+<https://gerrit-review.googlesource.com/Documentation/config-hooks.html>`__
+are distinct from Git hooks). Setting up ``git-multimail`` on a Gerrit
+installation can be done following the instructions below.
+
+The explanations show an easy way to set up ``git-multimail``,
+but leave ``git-multimail`` installed and unconfigured for a while. If
+you run Gerrit on a production server, it is advised that you
+execute the step "Set up the hook" last to avoid confusing your users
+in the meantime.
+
+Set up the hook
+---------------
+
+Create a directory ``$site_path/hooks/`` if it does not exist (if you
+don't know what ``$site_path`` is, run ``gerrit.sh status`` and look
+for a ``GERRIT_SITE`` line). Either copy ``git_multimail.py`` to
+``$site_path/hooks/ref-updated`` or create a wrapper script like
+this::
+
+  #! /bin/sh
+  exec /path/to/git_multimail.py "$@"
+
+In both cases, make sure the file is named exactly
+``$site_path/hooks/ref-updated`` and is executable.
+
+(Alternatively, you may configure the ``[hooks]`` section of
+gerrit.config)
+
+Configuration
+-------------
+
+Log on the gerrit server and edit ``$site_path/git/$project/config``
+to configure ``git-multimail``.
+
+Troubleshooting
+---------------
+
+Warning: this will disable ``git-multimail`` during the debug, and
+could confuse your users. Don't run on a production server.
+
+To debug configuration issues with ``git-multimail``, you can add the
+``--stdout`` option when calling ``git_multimail.py`` like this::
+
+  #!/bin/sh
+  exec /path/to/git-multimail/git-multimail/git_multimail.py \
+    --stdout "$@" >> /tmp/log.txt
+
+and try pushing from a test repository. You should see the source of
+the email that would have been sent in the output of ``git push`` in
+the file ``/tmp/log.txt``.