📝 Fix Uvicorn link in README

Author: tiangolo

README.md

@@ -82,7 +82,7 @@ FastAPI CLI takes the path to your Python program and automatically detects the
 
 For production you would use `fastapi run` instead. 🚀
 
-Internally, **FastAPI CLI** uses <a href="" class="external-link" target="_blank">Uvicorn</a>, a high-performance, production-ready, ASGI server. 😎
+Internally, **FastAPI CLI** uses <a href="https://www.uvicorn.org" class="external-link" target="_blank">Uvicorn</a>, a high-performance, production-ready, ASGI server. 😎
 
 ## `fastapi dev`