DOC: Fix docstring quotes in pandas.PeriodIndex
I am trying to work on fixing the docstring errors GL01 and GL02. The `validate_docstrings.py` gave a lot of them so I picked `pandas.PeriodIndex`:
```
pandas.PeriodIndex.day: Docstring text (summary) should start in the line immediately after the opening quotes (not in the same line, or leaving a blank line in between)
pandas.PeriodIndex.day: Closing quotes should be placed in the line after the last text in the docstring (do not close the quotes in the same line as the text, or leave a blank line between the last text and the quotes)
pandas.PeriodIndex.dayofweek: Docstring text (summary) should start in the line immediately after the opening quotes (not in the same line, or leaving a blank line in between)
pandas.PeriodIndex.dayofweek: Closing quotes should be placed in the line after the last text in the docstring (do not close the quotes in the same line as the text, or leave a blank line between the last text and the quotes)
pandas.PeriodIndex.dayofyear: Docstring text (summary) should start in the line immediately after the opening quotes (not in the same line, or leaving a blank line in between)
pandas.PeriodIndex.dayofyear: Closing quotes should be placed in the line after the last text in the docstring (do not close the quotes in the same line as the text, or leave a blank line between the last text and the quotes)
pandas.PeriodIndex.days_in_month: Docstring text (summary) should start in the line immediately after the opening quotes (not in the same line, or leaving a blank line in between)
pandas.PeriodIndex.days_in_month: Closing quotes should be placed in the line after the last text in the docstring (do not close the quotes in the same line as the text, or leave a blank line between the last text and the quotes)
pandas.PeriodIndex.daysinmonth: Docstring text (summary) should start in the line immediately after the opening quotes (not in the same line, or leaving a blank line in between)
pandas.PeriodIndex.daysinmonth: Closing quotes should be placed in the line after the last text in the docstring (do not close the quotes in the same line as the text, or leave a blank line between the last text and the quotes)
pandas.PeriodIndex.hour: Docstring text (summary) should start in the line immediately after the opening quotes (not in the same line, or leaving a blank line in between)
pandas.PeriodIndex.hour: Closing quotes should be placed in the line after the last text in the docstring (do not close the quotes in the same line as the text, or leave a blank line between the last text and the quotes)
pandas.PeriodIndex.minute: Docstring text (summary) should start in the line immediately after the opening quotes (not in the same line, or leaving a blank line in between)
pandas.PeriodIndex.minute: Closing quotes should be placed in the line after the last text in the docstring (do not close the quotes in the same line as the text, or leave a blank line between the last text and the quotes)
pandas.PeriodIndex.month: Docstring text (summary) should start in the line immediately after the opening quotes (not in the same line, or leaving a blank line in between)
pandas.PeriodIndex.month: Closing quotes should be placed in the line after the last text in the docstring (do not close the quotes in the same line as the text, or leave a blank line between the last text and the quotes)
pandas.PeriodIndex.quarter: Docstring text (summary) should start in the line immediately after the opening quotes (not in the same line, or leaving a blank line in between)
pandas.PeriodIndex.quarter: Closing quotes should be placed in the line after the last text in the docstring (do not close the quotes in the same line as the text, or leave a blank line between the last text and the quotes)
pandas.PeriodIndex.second: Docstring text (summary) should start in the line immediately after the opening quotes (not in the same line, or leaving a blank line in between)
pandas.PeriodIndex.second: Closing quotes should be placed in the line after the last text in the docstring (do not close the quotes in the same line as the text, or leave a blank line between the last text and the quotes)
pandas.PeriodIndex.week: Docstring text (summary) should start in the line immediately after the opening quotes (not in the same line, or leaving a blank line in between)
pandas.PeriodIndex.week: Closing quotes should be placed in the line after the last text in the docstring (do not close the quotes in the same line as the text, or leave a blank line between the last text and the quotes)
pandas.PeriodIndex.weekday: Docstring text (summary) should start in the line immediately after the opening quotes (not in the same line, or leaving a blank line in between)
pandas.PeriodIndex.weekday: Closing quotes should be placed in the line after the last text in the docstring (do not close the quotes in the same line as the text, or leave a blank line between the last text and the quotes)
pandas.PeriodIndex.weekofyear: Docstring text (summary) should start in the line immediately after the opening quotes (not in the same line, or leaving a blank line in between)
pandas.PeriodIndex.weekofyear: Closing quotes should be placed in the line after the last text in the docstring (do not close the quotes in the same line as the text, or leave a blank line between the last text and the quotes)
pandas.PeriodIndex.year: Docstring text (summary) should start in the line immediately after the opening quotes (not in the same line, or leaving a blank line in between)
pandas.PeriodIndex.year: Closing quotes should be placed in the line after the last text in the docstring (do not close the quotes in the same line as the text, or leave a blank line between the last text and the quotes)
```

However I need some help navigating to the related docstrings for each of these attributes. I thought I could find the `PeriodIndex` class at `pandas.core.indexes.period` which I did but I can't find any of the attributes (so the docstrings) in that file.

I am fairly new to contributing to Pandas so maybe I am making a dumb mistake or looking at the wrong place so I would appreciate some guidance.

Thanks!











