`koji-osbuild` is missing from the developer guides

[supakeen]

The projects overview in the developer guides should include koji-osbuild.

[ochosi]

True. Hadn't pulled that in because we're mostly handling it with the Koji maintainers directly. I don't expect a wider audience to take an interest in this - would you?
(Also want to avoid to clutter the development section too much, which is why more projects from GitHub aren't there at this point..)