Change URL, ensure guidelines conformity

Since we have now moved this repository from Alphagov to GDS Operations, we
should change the old URL to the new one, despite 301s existing, and ensure
we conform to our own guidelines for open-source projects (published at
http://gds-operations.github.io/guidelines/)
Merge pull request #19 from gds-operations/fix-url

Change URL, ensure guidelines conformity