Missing documentation about the eventMap

[green-coder]

Hi, nice little lib.

I noticed that you forgot to document in the readme.md the other way to listen to events, using the eventMap.

[cklmercer]

Thanks for pointing this out. Feel free to submit a documentation PR. Otherwise I'll try to get to this when I get a little free time.

[DaniJG]

Added a PR for this: #19

[DaniJG]

@cklmercer would it be worth pushing a new version to npm, just so the documentation is also up to date in npm?