Update README.md

[indigojump]

Got this on my first closeio run

$ tap-closeio --config ~/configs/closeio.config 
Traceback (most recent call last):
  File "/home/vagrant/.virtualenvs/close-tap/bin/tap-closeio", line 11, in <module>
    sys.exit(main())
  File "/home/vagrant/.virtualenvs/close-tap/local/lib/python3.4/site-packages/tap_closeio/__init__.py", line 181, in main
    config, state = utils.parse_args(REQUIRED_CONFIG_KEYS)
  File "/home/vagrant/.virtualenvs/close-tap/local/lib/python3.4/site-packages/tap_closeio/utils.py", line 56, in parse_args
    check_config(config, required_config_keys)
  File "/home/vagrant/.virtualenvs/close-tap/local/lib/python3.4/site-packages/tap_closeio/utils.py", line 69, in check_config
    raise Exception("Config is missing required keys: {}".format(missing_keys))
Exception: Config is missing required keys: ['start_date']

[cmerrick]

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[cmerrick]

You did it @indigojump!

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