The common problems that users ran into is that they are not
able to access the container's console in browser (via Horizon).
The reason is that the ws_proxy's URL is not accessible from
the browser. Either the configured IP address is not accessible
from outside or the port was blocked. This patch adds a note to
explain how to configure the websocket proxy's URL propertly.
Change-Id: Ifac45550f22409c2348e1b14ff46606a7bf09a89
e5a9190e1c