Update container_registry.md

doc/administration/container_registry.md

@@ -122,7 +122,9 @@ Registry is exposed to the outside world is `4567`, here is what you need to set
 in `gitlab.rb` or `gitlab.yml` if you are using Omnibus GitLab or installed
 GitLab from source respectively.
 
-N.B. Do not choose port 5000, it will conflict with the Docker registry service.
+>**Note:**
+Be careful to choose a port different than the one that Registry listens to (`5000` by default),
+otherwise you will run into conflicts .
 
 ---