git-for-each-repo: add page (#5490)

pages/common/git-for-each-repo.md

@@ -0,0 +1,13 @@
+# git for-each-repo
+
+> Run a Git command on a list of repositories.
+> Note: this command is experimental and may change.
+> More information: <https://git-scm.com/docs/git-for-each-repo>.
+
+- Run maintenance on each of a list of repositories stored in the `maintenance.repo` user configuration variable:
+
+`git for-each-repo --config={{maintenance.repo}} {{maintenance run}}`
+
+- Run `git pull` on each repository listed in a global configuration variable:
+
+`git for-each-repo --config={{global_configuration_variable}} {{pull}}`