[SPARK-14058][PYTHON] Incorrect docstring in Window.order

## What changes were proposed in this pull request?

Replaces current docstring ("Creates a :class:`WindowSpec` with the partitioning defined.") with "Creates a :class:`WindowSpec` with the ordering defined."

## How was this patch tested?

PySpark unit tests (no regression introduced). No changes to the code.

Author: zero323 <matthew.szymkiewicz@gmail.com>

Closes #11877 from zero323/order-by-description.