git-branch.txt: compare --contains, --merged and --no-merged

Signed-off-by: Lars Hjemli <hjemli@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-branch.txt

@@ -120,6 +120,15 @@ OPTIONS
 --no-track::
 	Ignore the branch.autosetupmerge configuration variable.
 
+--contains <commit>::
+	Only list branches which contain the specified commit.
+
+--merged::
+	Only list branches which are fully contained by HEAD.
+
+--no-merged::
+	Do not list branches which are fully contained by HEAD.
+
 <branchname>::
 	The name of the branch to create or delete.
 	The new branch name must pass all checks defined by
@@ -177,6 +186,18 @@ If you are creating a branch that you want to immediately checkout, it's
 easier to use the git checkout command with its `-b` option to create
 a branch and check it out with a single command.
 
+The options `--contains`, `--merged` and `--no-merged` serves three related
+but different purposes:
+
+- `--contains <commit>` is used to find all branches which will need
+  special attention if <commit> were to be rebased or amended, since those
+  branches contain the specified <commit>.
+
+- `--merged` is used to find all branches which can be safely deleted,
+  since those branches are fully contained by HEAD.
+
+- `--no-merged` is used to find branches which are candidates for merging
+  into HEAD, since those branches are not fully contained by HEAD.
 
 Author
 ------