Add links to test data bow@banff (GRAHAM / copernicus)

[bartvanosnabrugge]

description for the package branch a test case is made that does not download the raw data (especially the ERA5 data is too time consuming for an easy test). Therefore data from the download steps needs to be available from elsewhere.

use case as a cwarhm tester I want to not have to wait for the slow download processes so that I can assess the current cwarhm quicker and don't get frustrated with wait times on my initial try

• copernicus
• graham
• publicly available subset of the subset (first step preprocessed ERA5 only) on sharepoint or the like
• update readme file to link to data locations

Further improvements (possible follow up issues to create:)

• limit test data to only ERA5, other downloads through CWARHM download scripts