Make lead-up announcements that v2 onions will not work anymore

You're going to break lots of links in onionland and anger lots of people. In the clearnet, even basic http is still accessible for redirecting to https+TLS.

On every release leading up to July's stable release, make repeated announcements that v2 onions will not work anymore in the stable release starting in July. Write it in bold text. Write it repeatedly and/or keep it highly visible where users will see it:

• in a banner on about:tor inside the browser
• in every blog post of a TBB release leading up to it
• on the app stores
• on social media
• on the mailing lists
• in the changelog

"ATTENTION: v2 onion services will not work anymore in the stable release of Tor Browser starting in July. Please migrate to v3 onion services and update your bookmarks."