updated DataFrame.equals docstring
- [x] closes #29408
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Note: I tested the documentation locally and the links to assert_*_equals are working now.
Can you post a screenshot of how this appears locally? Somewhat surprised this renders the links <img width="1198" alt="Screenshot 2019-11-09 at 11 29 31" src="https://user-images.githubusercontent.com/17853006/68527196-a73fd980-02e4-11ea-8e54-97db8f5b50b0.png">
 Thanks @SaturnFromTitan 