docs: clarify issuer URL changes

[aeneasr]

Related Issue or Design Document

Checklist

• I have read the contributing guidelines and signed the CLA.
• I have referenced an issue containing the design document if my change introduces a new feature.
• I have read the security policy.
• I confirm that this pull request does not address a security vulnerability.
  If this pull request addresses a security vulnerability,
  I confirm that I got approval (please contact [email protected]) from the maintainers to push the changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added the necessary documentation within the code base (if appropriate).

Further comments

[vinckr]

its a bit vague for me when I need to do this.
"in some cases" - "it can be the case"

When do I need to change it:

1. Always in the cases listed (primary CNAME changed/old project)
2. If there is an error in OAuth2 and the cases listed apply (primary CNAME changed/old project)
   ?

[aeneasr]

that makes sense, thanks, will try to clarify

[aeneasr]

Done