Since I couldn't find a codename preference, I went with "Desitter"
(even though the correct spelling is "De Sitter"). There's a joke in
here that if we mess up and need a 5.1 release quickly, we could
codename it "anti-Desitter" :)

The release notes go as follows:
    <a href="download.html#release_5.0">FFmpeg 5.0 "Desitter"</a>, a new
    major release, is now available! For this long-overdue release, a major effort
    underwent to remove the old encode/decode APIs and replace them with an
    N:M-based API, the entire libavresample library was removed, libswscale
    got a new, easier to use AVframe-based API, the Vulkan code was much improved,
    many new filters were added, including libplacebo integration, and finally,
    DoVi support was added, including tonemapping and remuxing.
    Some of the changelog highlights:
    <changelog goes here>

The 'N' dates on the news entry and the download page
should be substituted with whenever we tag the release
and make the signed archives.

Patch attached.