docs for InfluxDBClusterClient

Signed-off-by: Can ZHANG <[email protected]>

README.rst

@@ -126,6 +126,20 @@ Here's a basic example (for more see the examples directory)::
 
     >>> print("Result: {0}".format(result))
 
+If you want to connect to a cluster, you could initialize a ``InfluxDBClusterClient``::
+
+    $ python
+
+    >>> from influxdb import InfluxDBClusterClient
+
+    >>> cc = InfluxDBClusterClient(hosts = [('192.168.0.1', 8086),
+                                            ('192.168.0.2', 8086),
+                                            ('192.168.0.3', 8086)],
+                                   username='root',
+                                   password='root',
+                                   database='example')
+
+``InfluxDBClusterClient`` has the same methods as ``InfluxDBClient``, it basically is a proxy to multiple InfluxDBClients.
 
 Testing
 =======