Add High Resolution Settlement Layer as data source for auxiliary raster

[iki77]

Currently, the documentation of masked area interpolation only reference NLCD as the data source.

High Resolution Settlement Layer (HRSL) should be added as alternative data source in the documentation, especially if the data is outside of the US

[knaaptime]

hi, thanks for this. We do have an example that uses copernicus which provides international raster data, but would certainly welcome examples from other sources! Any chance you'd like to put a pull request together?

[iki77]

Do you mean to add new examples from the pull request?

I think including links to other data sources besides NLCD is sufficient for me, because it is hard to find it as a beginner myself.