DOC: add staircase to pandas ecosystem page in docs

[venaturum]

staircase has been on a trajectory to operate as part of the pandas ecosystem.

With support for extension data types, extension arrays, and Series accessor several months ago, this journey has reached completion.

May it be added to the pandas ecosystem doc page?

Proposed additions:

Domain Specific

staircase is a data analysis package, built upon pandas and numpy, for modelling and manipulation of mathematical step functions. It provides a rich variety of arithmetic operations, relational operations, logical operations, statistical operations and aggregations for step functions defined over real numbers, datetime and timedelta domains.

Accessors

staircase sc Series provides methods for querying, aggregating and plotting step functions