release notes for 0.3.1 need to be written

[Will Kahn-Greene]

We need to write up the release notes for 0.3.1.

Three things it should note:

1. any changes that break someone's existing 0.3.0 instance
2. any thing a mediagoblin site admin should do to upgrade their 0.3.0 instance to 0.3.1
3. new features in 0.3.1
4. anything else that someone should know about 0.3.1

I added a stub to docs/source/siteadmin/relnotes.rst for this.

[Will Kahn-Greene]

Chris did this, so I'm marking this closed.