fix: replace broken Discord badge with shields.io badge (#67)

The dcbadge.vercel.app service was returning a broken image for the
Discord badge. Switch to shields.io which is more reliable and
consistent with the other badges in the README.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: danieljrc888

README.md

@@ -1,7 +1,7 @@
 # GenLayerPY
 
 [![License: MIT](https://img.shields.io/badge/License-MIT-green.svg)](https://opensource.org/license/mit/)
-[![Discord](https://dcbadge.vercel.app/api/server/8Jm4v89VAu?compact=true&style=flat)](https://discord.gg/qjCU4AWnKE)
+[![Discord](https://img.shields.io/badge/Discord-Join%20Us-7289da?logo=discord&logoColor=white)](https://discord.gg/qjCU4AWnKE)
 [![Twitter](https://img.shields.io/twitter/url/https/twitter.com/genlayerlabs.svg?style=social&label=Follow%20%40GenLayer)](https://x.com/GenLayer)