adds CODEOWNERS

.github/CODEOWNERS

@@ -0,0 +1,8 @@
+# This is a comment.
+# Each line is a file pattern followed by one or more owners.
+
+# These owners will be the default owners for everything in
+# the repo. Unless a later match takes precedence,
+# @phiwuu, @florianschanda and @christophkloeffel will be requested for
+# review when someone opens a pull request.
+*       @phiwuu @florianschanda @christophkloeffel