git-delete-merged-branches: add page

pages/common/git-delete-merged-branches.md

@@ -0,0 +1,9 @@
+# git delete merged branches
+
+> Delete branches that are listed in `git branch --merged` excluding master.
+> Part of `git-extras`.
+> More information: <https://github.com/tj/git-extras/blob/master/Commands.md#git-delete-merged-branches>.
+
+- Delete merged branches:
+
+`git delete-merged-branches`