docs: Include example implementation in MODPACK_GUIDE

Author: TheBossMagnus

MODPACK_GUIDE.md

@@ -16,6 +16,8 @@ Setup is straightforward:
 │ │ └─ config/
 │ │ └─ myMod.json (the "real" one)
 
+This is an [example implementation](https://github.com/TheBossMagnus/Thunder) (my modpack).
+
 ---
 
 ## FAQ
@@ -33,4 +35,4 @@ Setup is straightforward:
 
 **Q: Can I use this for other content than config files (e.g., .jar files)?**  
 **A:** Technically yes, there are no restrictions.  
-**Not recommended** as this mod is not designed for that, and it may confuse users.
+**Not recommended** as this mod is not designed for that, and it may confuse users.