Follow-up from "Group SSO Docs: Add OneLogin notes"

The following discussion from !18704 (merged) should be addressed:

• @eread started a discussion:

  Could I ask, could you specify what directory we mean? For example, ... in the OneLogin directory.

  Also, I know this page is all for .com, but you could be explicit here is as well?

  So for example:

  The GitLab app listed in the OneLogin directory is for self-managed GitLab instances.
  For GitLab.com, use a generic SAML Test Connector.

  Lastly, it's customary to not start a section with a note. If you want to lead with this information, feel free to make it plain text. If it is meant to be a "by the way", then you can add it further down.