Custom Option

I have a client who only needs to update one link. We were going to hide or remove the whole admin from his site since our client base is not comfortable with markup or html, and we'll need to not give them the admin until we figure out how to get tinymce in there. I figured out how to create a user that can just login, but I need to allow them to enter and save a link and then their theme needs to access and use that link. Any suggestions? I'm assuming a plugin would work best?

Sorry, markdown not markup, it's still early here ;)

Admin currently does not have ACL up to a page. Could be a good improvement, maybe add this as an issue on https://github.com/getgrav/grav-plugin-admin/issues to discuss

I ended up putting the link in a yaml in the config and then externally updating it. I could have done a form within the site to update it as well, I suppose.
Thanks for the help!