Add: Announcement post for 15.0-RC3 (#366)

Author: 2TallTyler

_posts/2025-12-20-openttd-15-0-rc3.md

@@ -0,0 +1,16 @@
+---
+title: OpenTTD 15.0-RC3
+author: 2TallTyler
+---
+
+Third try's the charm? We hope so; here's our third release candidate for OpenTTD 15.
+
+Most notably, the game no longer forgets your script configuration, and we've also fixed some rare crashes. See the changelog for the full list.
+
+As always, if you spot any more bugs, please [report them here](https://github.com/OpenTTD/OpenTTD/issues/new/choose).
+
+If you're one of our valued translators, this is the last call for translations for OpenTTD 15! 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-RC3/changelog.md)
+* [Bug tracker](https://github.com/OpenTTD/OpenTTD/issues)