Add CODEOWNERS to enable automatic review-requests

Since this only serves the purpose of GH review automation, it belongs
in out of sight in the .github repo. If this one day becomes useful
for other purposes as well, we can always move it later.

.github/CODEOWNERS

@@ -0,0 +1,2 @@
+# By default, everything goes to rpm-team
+*	@rpm-software-management/rpm-team