Reminder: The terms of service apply here too.
Logo design credit goes to: tubbadu
No such thing currently exists within Lemmy. It isn't a big deal to make a new community and do whatever you want with it. Or if all you want is a single post you could make a wiki community and set it to moderators only posting and then curate posts yourself as requested.
There is currently no /c/wiki community so it is free for the taking.
A wiki feature would be great
I bet there are services you can use to host a wiki, after that you can add a link to the description of the community. Seems a reasonable workaround, it will be quite confusing for a bit until enough people do it that a straightforward approach is adopted by most servers.
Check static website generators: https://jamstack.org/
For hosting: GitHub pages, Codeberg pages, Netlify, Cloudflare pages...
Git-based wikis are the best IMHO.
Right now, the only method is to use a specific community for this, use sticky posts, or use an external tool.