Adds convenience scripts to download coastline and landuse data

[daniel-j-h]

Splitting off from #720 - this changeset adds my convenience scripts to download coastline and landcover data. It's inconvenient to go to these websites, manually find the dataset needed, download and unpack it, and so on.

Let me know what a good file structure is, where we should put them, if I should consolidate them into a single script, and so on.

Adding a section to the readme; preview:

https://github.com/daniel-j-h/tilemaker/tree/add-coastline-landcover-download?tab=readme-ov-file#coastline-and-landcover

[daniel-j-h]

Adding here that in the past I have also used

https://daylightmap.org/2023/10/11/landcover.html

but long term this seems to get folded into the Overture distribution.

[systemed]

Superb, thank you. Happy to go with this as it is!