Update README regarding overlapping cidr limitation

Overlapping cidrs are supported only via passing pool names using
docker options. Same is being updated in README.

Change-Id: Ia59152e1ddc61560b1ce4af807621add337cf979
Closes-bug: #1596183

README.rst

@@ -158,3 +158,33 @@ website.
 
     $ cd build/html
     $ python -m SimpleHTTPServer 8080
+
+Limitations
+-----------
+
+To create Docker networks with subnets having same/overlapping cidr, it is
+expected to pass unique pool name for each such network creation Docker
+command. Docker cli options -o and --ipam-opt should be used to pass pool
+names as shown below:
+
+::
+
+    $ sudo docker network create --driver=kuryr --ipam-driver=kuryr \
+      --subnet 10.0.0.0/16 --ip-range 10.0.0.0/24 \
+      -o neutron.pool.name=neutron_pool1 \
+      --ipam-opt=neutron.pool.name=neutron_pool1 \
+      foo
+      eddb51ebca09339cb17aaec05e48ffe60659ced6f3fc41b020b0eb506d364
+
+Now Docker user creates another network with same cidr as the previous one,
+i.e 10.0.0.0/16, but with different pool name, neutron_pool2:
+
+::
+
+    $ sudo docker network create --driver=kuryr --ipam-driver=kuryr \
+      --subnet 10.0.0.0/16 --ip-range 10.0.0.0/24 \
+      -o neutron.pool.name=neutron_pool2 \
+      --ipam-opt=neutron.pool.name=neutron_pool2 \
+      bar
+      397badb51ebca09339cb17aaec05e48ffe60659ced6f3fc41b020b0eb506d786
+