Update python_web_app.rst

Fixed typo in the WEB_PORT command, missing sudo in front of docker command

docs/sources/examples/python_web_app.rst

@@ -86,7 +86,7 @@ http://0.0.0.0:5000/" in the log output.
 
 .. code-block:: bash
 
-    WEB_PORT=$(docker port $WEB_WORKER 5000)
+    WEB_PORT=$(sudo docker port $WEB_WORKER 5000)
 
 Look up the public-facing port which is NAT-ed. Find the private port
 used by the container and store it inside of the WEB_PORT variable.