Add GitHub codeowners file

[JamyGolden]

This automatically tags maintainers when a PR or issue is created

[belak]

How's this going to work, since I'm currently the only member of the base16-emacs group? 😆

[JamyGolden]

You'll be tagged automatically :p We should set things up so that the team is tagged because you may not always be the only maintainer and currently someone would have to manually tag you.

[belak]

I was more joking about what am I supposed to do when I submit pull requests :laughing:

[JamyGolden]

Haha oh right :smile: I just woke up :sleepy: