Update CODEOWNERS

Mentioned by @dholbach weaveworks#398 (comment)
I'm not sure if something more granular than this makes any sense.

Author: stealthybox

.github/CODEOWNERS

@@ -2,5 +2,7 @@
 # Each line is a file pattern followed by one or more owners.
 
 # These owners will be the default owners for everything in the repo.
+*       @chanwit
 *       @luxas
+*       @stealthybox
 *       @twelho