Update README.md

Add how to redirect web sockets for Bokeh app.

src/nectarchain/dqm/vm/README.md

@@ -35,6 +35,8 @@ Congrats! You now have two VMs with ZODB/ZEO servers with ZRS replication enable
 The Bokeh service is launched from the second VM (the one hosting the secondary, read-only database) with:
 ```shell
 bokeh serve --num-procs $(grep -c ^processor /proc/cpuinfo) \
+            --allow-websocket-origin=<SECONDARY_HOST_IP_ADDRESS>:5006 \
+            --allow-websocket-origin=<DNS_ALIAS_FOR_SECONDARY_HOST>:5006 \
             --show bokeh_app
 ```
 and served on `localhost` on port 5006.