Dataset: clean up and document the input data download description

[marlens123]

• Specify in the repo how a user can download the pre-training input data from Google Earthengine
• Specify in the repo how a user can download the evaluation input data from Google Earthengine (on hold until data is accessible)
• Create .zip with the right filenames, change dependencies (remove projection naming from README) (on hold until data is accessible)
• edit evaluation documentation for better readability (on hold until data is accessible)
• Write README for checkpoint storage