I discovered that under Account → App Tokens there is a nice simple way to add user names for Twitter and Github, and that doing so will cause my hosted blog to include rel=“me” links to those sites. It would be great if we could also do this for Mastodon usernames.
I don’t know if this is on the roadmap or not, but one relatively easy way to add the link is by installing the Meta tags plug-in and pasting the link element in the plug-in’s settings.
I’ve been thinking that the existing Twitter/Instagram/GitHub usernames under App Tokens should be moved to a plug-in, and we could add Mastodon there too. Meta Tags is the best solution for now, though.