fix: python client docs consumer example code missing client object

[ericsyh]

Signed-off-by: Eric Shen ericshenyuhao@outlook.com

Motivation

In the client-libraries-python, the sample code of Consumer missing to create the client object which consumer object relies.

import pulsar

consumer = client.subscribe('my-topic', 'my-subscription')

Modifications

I added the client object code to the sample like below

import pulsar

client = pulsar.Client('pulsar://localhost:6650')

consumer = client.subscribe('my-topic', 'my-subscription')

Impact

No code change