Create verifications.html

[anticomputer]

Mastodon account verifications to serve out of raw.

[xcorail]

cc @eorpina @ffink

[anticomputer]

note: note now if we add Verification with a content of https://raw.githubusercontent.com/github/securitylab/main/mastodon/verifications.html to our Mastodon profile metadata, on a save and refresh it SHOULD show as a green/checkboxed link, and serve as account verification since the html is being served out of the github org namespace.

e.g. for my personal account this looks like:

Available at: https://infosec.exchange/settings/profile

[ffink]

Thanks @anticomputer! Indeed, looks like both are verified now: