This function stores an OpenTopgrapy key in a local .Renviron file. If the .Renviron file exists, the key will be appended. This will typically only need to be done once per machine.
set_opentopo_key(key)
An OpenTopography API Key as a character. For details on obtaining an OpenTopgraphy key see https://opentopography.org/blog/introducing-api-keys-access-opentopography-global-datasets.