Update README.rst

[BondarenkoArtur]

expdata_generator expects different argument name

All Submissions Basics:

• [x] Have you followed the guidelines in our Contributing document?
• [x] Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• [x] Have you checked all Issues to tie the PR to a specific one?

All Submissions Cores:

• [ ] Have you added an explanation of what your changes do and why you'd like us to include them?
• [ ] Have you written new tests for your core changes, as applicable?
• [ ] Have you successfully ran tests with your changes locally?
• [ ] Does your submission pass tests, including CircleCI, Travis CI, and AppVeyor?
• [ ] Does your submission have appropriate code coverage? The cutoff threshold is 95% by Coversall.

New Model Submissions:

• [ ] Have you created a <NewModel>.py in ~/pyhealth/models/?
• [ ] Have you created a <NewModel>_example.py in ~/examples/?
• [ ] Have you created a test_<NewModel>.py in ~/pyhealth/test/?
• [ ] Have you lint your code locally prior to submission?

[BondarenkoArtur]

And by the way, links in PR template aren't working

[zzachw]

Thanks for your interest in PyHealth. We have released a brand-new version of PyHealth. It includes more EHR datasets, health-related tasks, and state-of-the-art models. Welcome to try it out!