get.gov: Update content for when users don't see their domain

[gabydisarli]

Issue description

As a domain manager, I want to understand why I don't see my domains when I sign into the registrar so I can make sure my account is correctly linked.

We will be adding a link to the domains table on the dashboard if the domains table is empty in issue cisagov/manage.get.gov#2056 . That link will point to help content at https://get.gov/help/faq/#do-not-see-my-domain. The content linked here is helpful for legacy users mainly, however, other users who have simply linked the wrong login.gov account to .gov could use content to help them self serve

Acceptance criteria

• Content is added to google doc
• Updates made at get.gov

Additional context

Links to other issues

Relates to cisagov/manage.get.gov#2056