Release Notes: announce that git svn will be phased out

It poses a substantial maintenance burden, what with the need not only
to keep maintaining Perl, but also subversion (and apr, apr-util,
and swig, and the Perl bindings of subversion).

At the same time, less and less `git svn` tickets (and no PRs worth
talking about) have trickled in.

Therefore it is a good time to say good-bye to `git svn` and send it off
to a cozy, relaxing retirement on the beach. It has served us well and
can now go on to enjoy life instead of work.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

ReleaseNotes.md

@@ -43,6 +43,8 @@ Git for Windows is distributed with other components yet, such as Bash, zlib, cu
 
 Git for Windows v2.48.1 is the last version to ship with the i686 ("32-bit") variant of the installer, portable Git and archive. Only 32-bit MinGit will be built for future versions, [until April 2029](https://gitforwindows.org/32-bit).
 
+Due to persistent maintenance challenges and the community's limited engagement and usage, `git svn` support in Git for Windows will be phased out over the next few releases.
+
 ### New Features
 
 * Comes with [MinTTY v3.7.7](https://github.com/mintty/mintty/releases/tag/3.7.7).