Add reference to the medium article: "Plotting Airbnb prices Boston".

[alshan]

The article link: https://csboutique.medium.com/lets-plot-948ee80cfa5c?source=friends_link&sk=d9e7c7cfb6e60562fc3ea8da9111a37e

The link on the related shared datalore notebook: https://datalore.jetbrains.com/view/notebook/eifzdh96VYuNrcjuOpYPYr

Add this reference to the "examples" section on both pages:

• https://lets-plot.org/pages/features/geopandas.html
• https://lets-plot.org/pages/features/interactive_maps.html