Added missing credits

Reimplemented PR #2 because @TomHAnderson closed it for no reason, then suggested I tried again. 

This PR fixes the fact that @TomHAnderson outright stole an entire codebase, [changed the name](https://github.com/StukiOrg/oauth2-simple-client/commit/1ac181b6c906e0e7ba7d6e53674565508434f3da) then decided to remove all attribution. The conversation on #2 did end up with the license being changed back to include the original author which was nice, but there is a lot more work being heavily ignored here. 

Hopefully this will get the situation resolved.