Add Usersnap integration to segment.io

Please add Usersnap to segment.io, as discussed with @DirtyAnalytics 

Can't add a vector file to this comment, here's a high-res PNG instead.
![usersnap_1024](https://cloud.githubusercontent.com/assets/4850875/4105558/a472f6ba-31ac-11e4-83f4-13cbf25d53ac.png)