README: add achievement:fieldnotes tag

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -14,6 +14,7 @@ tags:
   - sponsor:openbmb        # VoxCPM voice + MiniCPM5 chat/coding
   - achievement:offbrand   # custom Pixi.js game UI, not stock Gradio
   - achievement:welltuned  # ships a published fine-tune (weiner-klein LoRA)
+  - achievement:fieldnotes # write-up of what we built + learned
 ---
 
 # ⚔️ Tiny Army