Add a simple key for the colors of the dots on the map

This image has the numbers and color values used.
https://twitter.com/CupOJoseph/status/1174701947565330436/photo/1

use a div with absolute position or something so its always visible.

Inspect the repository's interactive map page and existing map UI to find where a persistent legend could be placed. Review the linked image for the number and color mapping, then run the map and verify that the key remains visible while viewing the map and clearly identifies the dot colors.

Written by the indexing model from the issue text.