Add description to category in widget form and context condition form

Firstly, this module is awesome, it does exactly what I assumed it to do, such as allowing users to select the block layout on a node-by-node basis. Doing more work with it, I thought the module didn't have the ability to run multiple context field instances. That's when I discovered the category field. This makes the module even more awesome! I created a patch that adds descriptions on category to both the widget form and the context condition form. If you'd like, I can implement this as part of a help hook that builds off of the readme. Let me know if this patch needs different wording.

Thanks,
Nielsonm