doc/rl-2505: mention Emacs bump and removal

Author: jian-lin

nixos/doc/manual/release-notes/rl-2505.section.md

@@ -18,6 +18,11 @@
 - LLVM has been updated from LLVM 16 (on Darwin) and LLVM 18 (on other platforms) to LLVM 19.
   This introduces some backwards‐incompatible changes; see the [upstream release notes](https://releases.llvm.org/) for details.
 
+- Emacs has been updated to 30.1.
+  This introduces some backwards‐incompatible changes; see the NEWS for details.
+  NEWS can been viewed from Emacs by typing `C-h n`, or by clicking `Help->Emacs News` from the menu bar.
+  It can also be browsed [online](https://git.savannah.gnu.org/cgit/emacs.git/tree/etc/NEWS?h=emacs-30).
+
 - The default PHP version has been updated to 8.3.
 
 - The default Erlang OTP version has been updated to 27.
@@ -416,6 +421,8 @@
 
 - `docker_24` has been removed, as it was EOL with vulnerabilities since June 08, 2024.
 
+- Emacs 28 and 29 have been removed.
+
 - `containerd` has been updated to v2, which contains breaking changes. See the [containerd
   2.0](https://github.com/containerd/containerd/blob/main/docs/containerd-2.0.md) documentation for more
   details.