Replace FAQ item about pull requests

[jayvdb]

http://docs.coala.io/en/latest/Help/FAQ.html#what-are-those-things-failing-passing-on-my-pull-request

This should be a generic FAQ entry about "I need help contributing to coala" , directing them to http://api.coala.io

[sarthakchakerverty]

@jayvdb Can you please assign this issue to me. Thanks.