Docs apparently incomplete

[thiagorova]

Hi, and first of all thanks a lot for this package!

So, i was reading the node-cron docs today and I was not able to easily find what the CronJob methods were. I ended up figuring it out manually, but found it to be an unnecessary hurdle in an otherwise pretty good package.

If you don't have time to update the ReadMe or make a wiki, I can make a PR to add these methods to the ReadMe.