hero docker added pull step

docs/hero_mdbook_docker.md

@@ -76,6 +76,10 @@ Note that you will need to adjust the local path of the git repo and the docker
   sudo docker start herodocker
   ```
   - You can now run the previous line **docker exec** and continue your work.
+- If you need to update the docker Hero image, run the following line:
+    ```
+    docker pull ghcr.io/scottyeager/hero:latest
+    ```
 
 ## Questions and Feedback