Add: Announcement post for 15.0-RC4 (#367)

Author: 2TallTyler

_posts/2025-12-26-openttd-15-0-rc4.md

@@ -0,0 +1,16 @@
+---
+title: OpenTTD 15.0-RC4
+author: 2TallTyler
+---
+
+Third, er, Fourth try's the charm? You found some bugs that needed fixing before the full release of OpenTTD 15. Let's do one last (we hope) Release Candidate.
+
+We've fixed two crashes related to station windows and signs, a hang related to implicit orders, and have stopped cacti from dying off completely with some tree spread settings.
+
+As always, if you spot any more bugs, please [report them here](https://github.com/OpenTTD/OpenTTD/issues/new/choose).
+
+We've heard from many of our translators that they've finished their languages. If your language needs updating, it's the last chance! Check on your language [here](https://translator.openttd.org/project/openttd-master).
+
+* [Download](https://www.openttd.org/downloads/openttd-releases/testing.html)
+* [Changelog](https://cdn.openttd.org/openttd-releases/15.0-RC4/changelog.md)
+* [Bug tracker](https://github.com/OpenTTD/OpenTTD/issues)