docs(backend): add Docker instructions

backend/README.md

@@ -1,5 +1,12 @@
 # Forum Backend
+Build and run Docker container:
+```shell
+docker build -t forum-backend .
+docker run --rm -d -p 8000:8000 forum-backend:latest
 ```
+
+Run locally:
+```shell
 pip install -r requirements.txt
 uvicorn forum:app --reload
 ```