DOC: cleanup docstring for read_json and fix error in contribution guide
- [ ] closes #xxxx
- [ ] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

- Contribution Guide
    - fix incorrect paths to doc folder
- read_json()
    - add period to end of sentences
    - conform parameter types to project standard
    - add newlines for readability and consistency
    - for convert_dates parameter, fix typos and malformed description and add list as accepted type
    - make Returns section conform to project standard