docs enhancement

[thuydotm]

Many of the docs are using generate_terrain() to create sample data. This is good for visualization but not ideal for demonstrating the results in the docstring.

[ianthomas23]

This needs some preliminary research work to identify one or more geographic areas that can be used to demonstrate a number of xarray-spatial functions. The idea is that we could ship small example datasets within the git repo to be used for user docs, tutorials, etc.

[thuydotm]

Closing as stale.