doc: Add period to parameter description
- [ ] closes #xxxx
- [ ] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

```

there are a few errors left:
################################################################################
################################## Validation ##################################
################################################################################

11 Errors found:
        Parameters {'**fields', 'name', 'ordinal'} not documented
        Unknown parameters {'second', 'minute', 'year', 'month', 'quarter', 'hour', 'day'}
        Parameter "year" has no description
        Parameter "month" has no description
        Parameter "quarter" has no description
        Parameter "day" has no description
        Parameter "hour" has no description
        Parameter "minute" has no description
        Parameter "second" has no description
        Parameter "dtype" has no description
        Examples do not pass tests
```