git-gh-pages: add page (#8787)

pages/common/git-gh-pages.md

@@ -0,0 +1,9 @@
+# git gh-pages
+
+> Create a new branch inside the current repository called `gh-pages`.
+> Part of `git-extras`.
+> More information: <https://github.com/tj/git-extras/blob/master/Commands.md#git-gh-pages>.
+
+- Create the GitHub pages branch inside the repository in the current directory:
+
+`git gh-pages`