Add a CODEOWNERS file

Signed-off-by: Seth Chisamore <schisamo@chef.io>

.github/CODEOWNERS

+# Order is important. The last matching pattern has the most precedence.
+
+* @chef/omnibus-maintainers

.github/ISSUE_TEMPLATE.md

@@ -22,5 +22,3 @@ The relevant output of the Omnibus build or a link to a gist of the entire build
 The verbose build output (`omnibus build <PROJECT> -l internal`) may be useful, but please link to a gist, or truncate it.
 
 --------------------------------------------------
-/cc @chef/omnibus-maintainers <- This ensures the Omnibus Maintainers team are notified to review this PR.
-

.github/PULL_REQUEST_TEMPLATE.md

@@ -3,7 +3,6 @@
 Briefly describe the new feature or fix here
 
 --------------------------------------------------
-/cc @chef/omnibus-maintainers <- This ensures the Omnibus Maintainers team are notified to review this PR.
 
 #### Maintainers