Allow custom content on the About page

Check before submitting

• I searched existing issues and did not find a duplicate

What problem would this solve?

Currently, the About page only shows the title of the instance. Below that, Memos automatically displays version information and project links. There's no way to add custom explanatory content, for example, contact info, usage guidelines, or a personal introduction.

What would you like to happen?

Please add a free-text field between the title section and the automatically generated Memos info/links section, where admins can write custom content, ideally using the same editor and rendering as a regular memo (Markdown support, same styling, same input experience).

This would let admins turn the About page into a proper, personalized landing page while keeping the built-in version/links block intact below it.

Additional context

No response