api: Remove unnecessary API key details.

Fixes #1.

zulip/examples/list-subscriptions

@@ -24,13 +24,13 @@
 from __future__ import print_function
 import argparse
 
-usage = """list-subscriptions --user=<bot's email address> --api-key=<bot's api key> [options]
+usage = """list-subscriptions [options]
 
 Prints out a list of the user's subscriptions.
 
-Example: list-subscriptions --user=username@example.com --api-key=a0b1c2d3e4f5a6b7c8d9e0f1a2b3c4d5
+Example: list-subscriptions
 
-You can omit --user and --api-key arguments if you have a properly set up ~/.zuliprc
+Specify your Zulip API credentials and server in a ~/.zuliprc file or using the options.
 """
 
 import zulip