Add: OpenTTD 15.0-beta2 announcement

Long social message (Reddit / Discord / TT-Forums):

```
It's time for another beta release preparing for OpenTTD 15.

It includes new features like individually-placed houses, more rocks, snowy rocks, and touchpad scrolling on Windows, plus a bunch of bugfixes.

Check it out and help us test!

https://www.openttd.org/news/2025/03/29/openttd-15-0-beta2.html
```

Short social message:
```
OpenTTD 15.0-beta2 now available on Steam / our website.
Place houses and look out for increased rocks.
https://www.openttd.org/news/2025/03/29/openttd-15-0-beta2.html
```

Steam:
Steam image coming soon, unless someone gets to it before me. 🙂

Author: 2TallTyler

_posts/2025-03-29-openttd-15-0-beta2.md

@@ -0,0 +1,22 @@
+---
+title: OpenTTD 15.0-beta2
+author: 2TallTyler
+---
+
+It's nearly April 1st, but bugs are no joke.
+
+We've fixed a bunch more since beta1, and need more testing. Also, we added some new features! Highlights include:
+* Snow-covered rocks are now visible
+* Steep hills now have more rocks generated during map generation or heightmap import
+* Houses can be individually placed by players (if enabled), and protected from towns upgrading them during growth
+* Touchpad two-finger map scrolling for Windows
+* A variety of bugfixes
+
+(As always, see the changelog for further details).
+
+The usual titlegame competition has been [announced on the forums](https://www.tt-forums.net/viewtopic.php?t=92166).
+See the page for the exact competition rules if you are interesed.
+
+* [Download](https://www.openttd.org/downloads/openttd-releases/testing.html)
+* [Changelog](https://cdn.openttd.org/openttd-releases/15.0-beta2/changelog.txt)
+* [Bug tracker](https://github.com/OpenTTD/OpenTTD/issues)