Add branch management for releases to gitworkflows

The current man page does a reasonable job at describing branch management
during the development process, but it does not contain any guidance as to
how the branches are affected by releases.

Add a basic introduction to the branch management undertaken during a
git.git release, so that a reader may gain some insight into how the
integration, maintenance, and topic branches are affected during the
release transition, and is thus able to better design the process for their
own project.

Other release activities such as reviews, testing, and creating
distributions are currently out of scope.

Signed-off-by: Nanako Shiraishi <nanako3@lavabit.com>
Acked-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/gitworkflows.txt

@@ -209,6 +209,121 @@ chance to see if their in-progress work will be compatible.  `git.git`
 has such an official throw-away integration branch called 'pu'.
 
 
+Branch management for a release
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Assuming you are using the merge approach discussed above, when you
+are releasing your project you will need to do some additional branch
+management work.
+
+A feature release is created from the 'master' branch, since 'master'
+tracks the commits that should go into the next feature release.
+
+The 'master' branch is supposed to be a superset of 'maint'. If this
+condition does not hold, then 'maint' contains some commits that
+are not included on 'master'. The fixes represented by those commits
+will therefore not be included in your feature release.
+
+To verify that 'master' is indeed a superset of 'maint', use git log:
+
+.Verify 'master' is a superset of 'maint'
+[caption="Recipe: "]
+=====================================
+git log master..maint
+=====================================
+
+This command should not list any commits.  Otherwise, check out
+'master' and merge 'maint' into it.
+
+Now you can proceed with the creation of the feature release. Apply a
+tag to the tip of 'master' indicating the release version:
+
+.Release tagging
+[caption="Recipe: "]
+=====================================
+`git tag -s -m "GIT X.Y.Z" vX.Y.Z master`
+=====================================
+
+You need to push the new tag to a public git server (see
+"DISTRIBUTED WORKFLOWS" below). This makes the tag available to
+others tracking your project. The push could also trigger a
+post-update hook to perform release-related items such as building
+release tarballs and preformatted documentation pages.
+
+Similarly, for a maintenance release, 'maint' is tracking the commits
+to be released. Therefore, in the steps above simply tag and push
+'maint' rather than 'master'.
+
+
+Maintenance branch management after a feature release
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+After a feature release, you need to manage your maintenance branches.
+
+First, if you wish to continue to release maintenance fixes for the
+feature release made before the recent one, then you must create
+another branch to track commits for that previous release.
+
+To do this, the current maintenance branch is copied to another branch
+named with the previous release version number (e.g. maint-X.Y.(Z-1)
+where X.Y.Z is the current release).
+
+.Copy maint
+[caption="Recipe: "]
+=====================================
+`git branch maint-X.Y.(Z-1) maint`
+=====================================
+
+The 'maint' branch should now be fast-forwarded to the newly released
+code so that maintenance fixes can be tracked for the current release:
+
+.Update maint to new release
+[caption="Recipe: "]
+=====================================
+* `git checkout maint`
+* `git merge --ff-only master`
+=====================================
+
+If the merge fails because it is not a fast-forward, then it is
+possible some fixes on 'maint' were missed in the feature release.
+This will not happen if the content of the branches was verified as
+described in the previous section.
+
+
+Branch management for next and pu after a feature release
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+After a feature release, the integration branch 'next' may optionally be
+rewound and rebuilt from the tip of 'master' using the surviving
+topics on 'next':
+
+.Rewind and rebuild next
+[caption="Recipe: "]
+=====================================
+* `git checkout next`
+* `git reset --hard master`
+* `git merge ai/topic_in_next1`
+* `git merge ai/topic_in_next2`
+* ...
+=====================================
+
+The advantage of doing this is that the history of 'next' will be
+clean. For example, some topics merged into 'next' may have initially
+looked promising, but were later found to be undesirable or premature.
+In such a case, the topic is reverted out of 'next' but the fact
+remains in the history that it was once merged and reverted. By
+recreating 'next', you give another incarnation of such topics a clean
+slate to retry, and a feature release is a good point in history to do
+so.
+
+If you do this, then you should make a public announcement indicating
+that 'next' was rewound and rebuilt.
+
+The same rewind and rebuild process may be followed for 'pu'. A public
+announcement is not necessary since 'pu' is a throw-away branch, as
+described above.
+
+
 DISTRIBUTED WORKFLOWS
 ---------------------