docs: remove NAT rule when removing bridge

Signed-off-by: imre Fitos <imre.fitos+github@gmail.com>

docs/sources/articles/networking.md

@@ -687,6 +687,7 @@ stopping the service and removing the interface:
     $ sudo service docker stop
     $ sudo ip link set dev docker0 down
     $ sudo brctl delbr docker0
+    $ sudo iptables -t nat -F POSTROUTING
 
 Then, before starting the Docker service, create your own bridge and
 give it whatever configuration you want.  Here we will create a simple
@@ -708,6 +709,14 @@ illustrate the technique.
         inet 192.168.5.1/24 scope global bridge0
            valid_lft forever preferred_lft forever
 
+    # Confirming outgoing NAT masquerade is setup
+
+    $ sudo iptables -t nat -L -n
+    ...
+    Chain POSTROUTING (policy ACCEPT)
+    target     prot opt source               destination
+    MASQUERADE  all  --  192.168.5.0/24      0.0.0.0/0
+
     # Tell Docker about it and restart (on Ubuntu)
 
     $ echo 'DOCKER_OPTS="-b=bridge0"' >> /etc/default/docker