Add essential documentation

[ksvan]

Essential documentation for people to really use this

• How Receieve function works
• How Emit function works
• How to provide credentials for config nodes using load()

[knolleary]

Can you clarify what you mean by emit? Nodes should use node.send to send messages. They shouldn't use the internal event emitter of the node for sending messages. Or do you have something else in mind?

[ksvan]

That’s actually a good answer on emit itself and what to use for what purpose:) I just saw it in some samples “out there” when trying to learn this. And i’m thinking only in the context of test-helper usage here btw.

[jensrossbach]

@knolleary I would also like to know how the credentials that can be passed as third argument to the load function must look like (i.e., what is the expected structure of the object to provide).