Add the pan-ARctic CAtchment DatabasE (ARCADE) dataset

[julietcohen]

Anna suggested adding the pan-ARctic CAtchment DatabasE (ARCADE) which represents watershed boundaries. This dataset is publicly available on DataverseNL. The accompanying paper is here.

The metadata for the dataset is not very specific about the differences between the files ARCADE_V1_36_1KM.ZIP and ARCADE_V1_37_1KM.ZIP. Reading in these shapefiles should reveal which is more applicable for the PDG, if not both.

ARCADE_V1_36_1KM.ZIP is 123.9 MB and described as:
"Shapefile of catchments draining into the Arctic Ocean, Strahler order 5 or up and at least 1km^2 area size. Now with mean and Sen-slope of annual maximum MOD13A1 v006 NDVI (2000-2021) instead of August mean."

ARCADE_V1_37_1KM.ZIP is 125.8 MB and described as:
"ARCADE_v1_37_1km, now includes CGLS-LC100v3 land cover product data."

Each has an excel sheet that describes the variables.

[julietcohen]

Closed as it is a duplicate. See issue#29.