Add docker.networks documentation (#828)

Co-authored-by: Joongi Kim <[email protected]>

docs/networks.rst

@@ -0,0 +1,44 @@
+==========
+Networks
+==========
+
+Create a network
+==================
+
+.. code-block:: python
+
+    import asyncio
+    import aiodocker
+
+    async def create_network():
+        docker = aiodocker.Docker()
+        network_config = {
+            "Name": "isolated_nw",
+            "Driver": "bridge",
+            "EnableIPv6": False,
+            "IPAM": {
+                "Driver": "default"
+            }
+        }
+        network = await docker.networks.create(config=network_config)
+        print(network)
+        await docker.close()
+
+    if __name__ == '__main__':
+        asyncio.run(create_network())
+
+---------
+Reference
+---------
+
+DockerNetworks
+================
+.. autoclass:: aiodocker.docker.DockerNetworks
+        :members:
+        :undoc-members:
+
+DockerNetwork
+===============
+.. autoclass:: aiodocker.docker.DockerNetwork
+        :members:
+        :undoc-members: