Explain docker run -p in README (re. #5) (#16)

README.md

@@ -1,4 +1,5 @@
 # fava-docker
+
 A Dockerfile for beancount-fava
 
 ## Environment Variable
@@ -7,16 +8,20 @@ A Dockerfile for beancount-fava
 
 ## Usage Example
 
-```
+```bash
 # assume you have example.bean in the current directory
 docker run -v $PWD:/bean -e BEANCOUNT_FILE=/bean/example.bean yegle/fava
 ```
 
+NOTE: The command above does not expose the Fava HTTP server port outside of Docker's internal network.
+This allows you [to use your own reverse proxy](https://github.com/beancount/fava/tree/main/contrib/docker#advanced).
+If you do want to expose the service without using a reverse proxy for local testing, you must add `-p 5000:5000`
+to access Fava on http://localhost:5000.
+
 ## Note on auto build
 
 The [docker image](https://hub.docker.com/r/yegle/fava) was switched
 from build by Docker Hub to Github Actions. The image label pattern is
 changed: instead of labeled `version-1.xx` it's now labeled `v1.xx`.
 
-You can check the auto build logs at
-https://github.com/yegle/fava-docker/actions
+You can check the auto build logs at https://github.com/yegle/fava-docker/actions.