git-repl: add page (#5974)

pages/common/git-repl.md

@@ -0,0 +1,21 @@
+# git repl
+
+> Git REPL (read-evaluate-print-loop) - an interactive Git shell.
+> Part of `git-extras`.
+> More information: <https://github.com/tj/git-extras/blob/master/Commands.md#git-repl>.
+
+- Start an interactive Git shell:
+
+`git repl`
+
+- Run a Git command while in the interactive Git shell:
+
+`{{git_subcommand}} {{command_arguments}}`
+
+- Run an external (non-Git) command while in the interactive Git shell:
+
+`!{{command}} {{command_arguments}}`
+
+- Exit the interactive Git shell (or press Ctrl + D):
+
+`exit`