DOC: TimeStamp.strftime() missing argument description
#### Location of the documentation

https://pandas.pydata.org/docs/dev/reference/api/pandas.Timestamp.strftime.html?highlight=strftime#pandas.Timestamp.strftime

#### Documentation problem

The argument for `TimeStamp.strftime()` is missing in the docs

#### Suggested fix for documentation

Argument is a format string.  Should reference python docs https://docs.python.org/3/library/datetime.html
