This changeset adds a `wp-admin/user/contribute.php` file to allow the "Get Involved" link to work on User Admin.
This changeset prevents an unintended 404 that occurs when a logged-in user clicks the "Get Involved" link (located in the menu-bar) from inside of the multisite-specific User Dashboard.
Related: r56220, r56309, #23348.
Props ignatiusjeroe, audrasjb, tobiasbg.
Fixes#61122.
Built from https://develop.svn.wordpress.org/trunk@58118
git-svn-id: http://core.svn.wordpress.org/trunk@57583 1a063a9b-81f0-0310-95a4-ce76da25c4cd
