Markdown release notes

[Michael Rienstra <mrienstra@gmail.com>]

Release notes are currently plain text files -- and that option should
surely remain for backwards compatibility -- but it would be nice to
have them in a format that facilitates cross-linking.

For example, https://git-scm.com/ currently shows:

> Latest source Release
> 2.39.1
> Release Notes (2022-12-13)


Which links to:

> Git v2.39.1 Release Notes
> =========================
>
>
> This release merges the security fix that appears in v2.30.7; see
>
> the release notes for that version for details.

-- https://raw.github.com/git/git/master/Documentation/RelNotes/2.39.1.txt

Navigating to the release notes for v2.30.7 is not convenient. Some
users will simply modify the URL, which will do the trick. Others may
find their way to
https://github.com/git/git/tree/master/Documentation/RelNotes & search
for "2.39.1", which also works, but isn't particularly friendly.

Markdown alternative POC for the v2.39.1 release notes:
https://github.com/mrienstra/git/blob/markdown-release-notes-poc/Documentation/RelNotes/2.39.1.md

Now "the security fix that appears in v2.30.7" can be easily followed to:
https://github.com/mrienstra/git/blob/markdown-release-notes-poc/Documentation/RelNotes/2.30.7.md

Along the same lines, CVE IDs could be linked out in Markdown release
notes, I did that in a few cases as part of this POC. For example, in
the v2.30.7 release notes (last link above) there is now a link to:
https://nvd.nist.gov/vuln/detail/CVE-2022-41903

(nvd.nist.gov seemed to be preferred over cve.org, based on a search
of http://public-inbox.org/git)

I used regex search & replace to add these links, sundry details are
in commit messages here:
https://github.com/git/git/compare/master...mrienstra:git:markdown-release-notes-poc

This seems like a simple change with no obvious side effects. I
suppose the Markdown files could be placed in a subfolder to prevent a
jump from 464 files to 928 in one directory.

Thoughts?