Sync up RTD with new ChannelWorm repo location

Seems like [the docs](http://channelworm.readthedocs.org/) are not syncing up anymore, probably because of the URL change recently. 
Specifically, [this page](https://github.com/openworm/ChannelWorm/blob/dev/docs/walkthrough.md) is not showing up. Should be a simple config fix on rtd.
