External Services -> GitHub requires a "url" field but doesn't tell you

Created by: slimsag

Start a clean instance. Add a GitHub external service connection like so:

No repositories will show up when you visit /site-admin/repositories; if you modify the entry to be:

Then it suddenly works.

Issues:

1. You are not informed that this is a required field anywhere.
2. The default when you ctrl+space select the url field appears to be https://github.com, but why is that default not actually applied when the field is omitted?

@nicksnyder I am assigning you because I don't know who should own this.