Docstring pandas.data frame.diff
Checklist for the pandas documentation sprint (ignore this if you are doing
an unrelated PR):

- [X] PR title is "DOC: update the <your-function-or-method> docstring"
- [X] The validation script passes: `scripts/validate_docstrings.py <your-function-or-method>`
- [X] The PEP8 style check passes: `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [X] The html version looks good: `python doc/make.py --single <your-function-or-method>`
- [X] It has been proofread on language by another sprint participant

Please include the output of the validation script below between the "```" ticks:

```
################################################################################
################################## Validation ##################################
################################################################################

Docstring for "pandas.DataFrame.diff" correct. :)
```

If the validation script still gives errors, but you think there is a good reason
to deviate in this case (and there are certainly such cases), please state this
explicitly.

I think we just need a `.` at the end of this line https://github.com/pandas-dev/pandas/pull/20227/files#diff-1e79abbbdd150d4771b91ea60a4e1cc7R4739

LGTM otherwise. I can definitely do that, but it won't be consistent with the other functions' documentation.

I'm also adding a "See Also" to DataFrame.pct_change() which I didn't realize was pretty much the same function using % instead of absolute value. As discussed, the "." was added at the end of the versionadded and passed validation without any errors. Hello @adatasetaday! Thanks for updating the PR.



Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on March 11, 2018 at 12:35 Hours UTC Thanks @adatasetaday!