DOC: Add Lux to Pandas Ecosystem page
#### Location of the documentation

List of systems under [pandas ecosystem](https://pandas.pydata.org/docs/ecosystem.html#pandas-ecosystem)

#### Documentation problem

Add [Lux](https://github.com/lux-org/lux) to the ["pandas ecosystem" documentation](https://pandas.pydata.org/docs/ecosystem.html#pandas-ecosystem)

