Update README.md

Added info about cred.php

README.md

@@ -1,2 +1,13 @@
 # net-neutral
 Facebook profile picture overlay creater 
+
+
+#credentials
+Please add a file named `cred.php` to the folder and add the following lines in them:
+
+```
+<?php
+$_YOUR_APP_ID = 'XYZ';
+$_YOUR_APP_SECRET = 'XYZ';
+?>
+```