Add third option to test site changes

README.md

@@ -107,7 +107,7 @@ of [https://docs.docker.com/](https://docs.docker.com/).
 
 ## Staging the docs
 
-You have two options:
+You have three options:
 
 1.  On your local machine, clone this repo and run our staging container:
 
@@ -169,7 +169,17 @@ You have two options:
     running on http://localhost:4000/ by default. To stop it, use `CTRL+C`.
     You can continue working in a second terminal and Jekyll will rebuild the
     website incrementally. Refresh the browser to preview your changes.
+    
+3. Build and run a Docker image for your working branch.
+    
+   ```bash
+   $ docker build -t docker build -t docs/docker.github.io:<branch_name> .
+   $ docker run --rm -it -p 4000:4000 docs/docker.github.io:<branch_name>
+    ```
 
+   After the `docker run` command, copy the URL provided in the container build output in a browser, 
+   http://0.0.0.0:4000, and verify your changes.
+   
 ## Read these docs offline
 
 To read the docs offline, you can use either a standalone container or a swarm service.