Update reference from fromString to parseString in docs

[perryh]

All Submissions:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

New Feature Submissions:

1. Have you added tests for the new feature
2. Does your submission pass tests?
3. Have you lint your code locally prior to submission?
4. Have you updated the docs?
   • If you added new parsing or formatting options have you added them to the docs?
   • If applicable have you added an example to the parsing or formatting docs?

Changes to Core Features:

• 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?