chore: update CODEOWNERS

Author: cloud-foundation-bot

CODEOWNERS

@@ -2,3 +2,11 @@
 # https://github.com/GoogleCloudPlatform/cloud-foundation-toolkit/blob/master/infra/terraform/test-org/org/locals.tf
 
 * @terraform-google-modules/cft-admins
+
+# NOTE: GitHub CODEOWNERS locations:
+# https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners#codeowners-and-branch-protection
+
+CODEOWNERS @terraform-google-modules/cft-admins
+.github/CODEOWNERS @terraform-google-modules/cft-admins
+docs/CODEOWNERS @terraform-google-modules/cft-admins
+