fix: add rel=me to mastodon

[SethFalco]

Minor pet peeve, but on Mastodon your site isn't verified because it doesn't have rel="me" in the HTML.

If you put a link in your profile metadata, Mastodon checks if the linked page links back to your Mastodon profile. If so, you get a verification checkmark next to that link, since you are confirmed as the owner.

Behind the scenes, Mastodon checks for the rel="me" attribute on the link back. Likewise, Mastodon puts rel="me" on the links within profile metadata.
— https://docs.joinmastodon.org/user/profile/

After this, it should display it as a verified link. That way users don't have to manually check the website to ensure this is the official account on Mastodon.