Add required social-media post link to README

Links the X launch post per the Build Small submission requirement
(social post showcasing the app, linked from the Space README).

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

README.md

@@ -18,7 +18,7 @@ tags:
 
 **Dump everything on your mind — get back what to do *first*, with the math shown.**
 
-[**▶ Live demo**](https://huggingface.co/spaces/build-small-hackathon/whatfirst-small)  ·  [what-first.com](https://what-first.com)  ·  Apache-2.0  ·  Runs 100% offline
+[**▶ Live demo**](https://huggingface.co/spaces/build-small-hackathon/whatfirst-small)  ·  [📣 Launch post](https://x.com/tbd_ntbd/status/2066222870657692128)  ·  [what-first.com](https://what-first.com)  ·  Apache-2.0  ·  Runs 100% offline
 
 A small **local** vision-language model (Qwen2.5-VL-3B, ~2 GB, running on
 llama.cpp) reads a messy brain-dump or a photo of a to-do list and turns each