Update ChatOps guide to highlight the username needs to match .com

doc/development/chatops_on_gitlabcom.md

@@ -13,7 +13,7 @@ tasks such as:
 
 To request access to Chatops on GitLab.com:
 
-1. Log into <https://ops.gitlab.net/users/sign_in> using the same username as for GitLab.com.
+1. Log into <https://ops.gitlab.net/users/sign_in> **using the same username** as for GitLab.com (you may have to rename it).
 1. Ask [anyone in the `chatops` project](https://gitlab.com/gitlab-com/chatops/-/project_members) to add you by running `/chatops run member add <username> gitlab-com/chatops --ops`.
 
 ## See also