BOOYA -> Github Drinkup

There's a [github drinkup](https://github.com/blog/1809-github-drinkup-in-oxford-uk) in town at the same time as this weeks meetup.

If we don't BOOYA, then we'll have enough time to jsoxford, then github drinkup.

I've also added a rules page - just in case anyone was thinking of skipping out of the meetup.  I'm pretty sure it's sound in some kind of legally binding way…