Add sample mysql_credentials file

mysql_credentials.php.sample

@@ -0,0 +1,8 @@
+<?php
+return array(
+  "servername" => "localhost",
+  "username" => "username_goes_here",
+  "password" => "password_goes_here",
+  "database" => "database_name_goes_here"
+);
+?>