workshops/models.py: Make Site.notes blank
workshops/models.py: Make Site.notes blank

On Thu, Feb 19, 2015 at 06:14:57AM -0800, Greg Wilson wrote [1]:
> The `notes` field in `Site` and `Event` is optional - people must
> not be required to fill it in when creating new sites or events.

[1]: https://github.com/swcarpentry/amy/issues/198

swcarpentry/amy,wking/swc-amy,vahtras/amy,wking/swc-amy,shapiromatron/amy,swcarpentry/amy,pbanaszkiewicz/amy,pbanaszkiewicz/amy,vahtras/amy,swcarpentry/amy,vahtras/amy,wking/swc-amy,shapiromatron/amy,shapiromatron/amy,wking/swc-amy,pbanaszkiewicz/amy