add pascal case hint

CONTRIBUTING.md

@@ -81,6 +81,7 @@ You can also send a mail to the [owncloud-devel mailing list](https://mailman.ow
   ```
 
 * Place a space before and after the parameter block for if, else, for, foreach, function
+* Everything should be in pascalCase except classes which should be in CamelCase
 
 ### Project Structure
 The project is structured in the following way: