added "berlin code of conduct" link

I'm totally :+1: in regard to referencing an existing code of conduct instead of compiling one ourselves. 

However, would it make more sense to refer to a wider, maybe even globally accepted code of conduct - if such a document exists - the local community would be willing to subscribe to?

As compiling a code of conduct is a recurring task for each and every conference out there, maybe some sort of standard, if you will, should exist.