Docs for watchEvent()

[doublejosh]

Looks like missing and/or incorrect docs for watchEvent() in snippets.

https://github.com/prescottprue/react-redux-firebase/blob/master/examples/snippets/watchEvent/README.md

Current behavior
It doesn't include the use of watchEvent() in the example.

[prescottprue]

Thanks for reaching out - the example in that folder actually uses watchEvent, but it wasn't mentioned in the README. This has been corrected