Minor README fix

[poflynn]

Fixed 'demo_iam.json' filename in step 3 to match the filename in step 2. I was getting the error below when I followed the instructions and it took me a while to notice the filename difference.

Traceback (most recent call last):
  File "/Users/paul.oflynn/workspace/venv/bin/cloudtracker", line 11, in <module>
    load_entry_point('cloudtracker==2.1.2', 'console_scripts', 'cloudtracker')()
  File "/Users/paul.oflynn/workspace/venv/lib/python3.7/site-packages/cloudtracker/cli.py", line 104, in main
    run(args, config, args.start, args.end)
  File "/Users/paul.oflynn/workspace/venv/lib/python3.7/site-packages/cloudtracker/__init__.py", line 436, in run
    account_iam = get_account_iam(account)
  File "/Users/paul.oflynn/workspace/venv/lib/python3.7/site-packages/cloudtracker/__init__.py", line 162, in get_account_iam
    return json.load(open(account['iam']))
FileNotFoundError: [Errno 2] No such file or directory: 'account-data/demo-iam.json'```

[poflynn]

No doubt the cause of #23 also..

[CLAassistant]

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[0xdabbad00]

Thank you for figuring that out and what was going on in #23! Can you agree to the CLA so I can accept this PR?

[poflynn]

Thank you for figuring that out and what was going on in #23! Can you agree to the CLA so I can accept this PR?

Hmm, I did sign it - twice in fact. When I click on the link now I get the msg "You have signed the CLA for duo-labs/cloudtracker". Not sure what else I can do?

[0xdabbad00]

I think the username or email address used for your git commit doesn't match your Github account, so that's why the CLA check isn't passing. Since you've stated here that you signed it, that's good enough for me as a record that you signed it.

[poflynn]

Ack, indeed, wrong email which I didn't want. Oh well, merged now so too late.

Thx for the awesome utility...