Make "user instructions" for module leaders for uploading data

[eevasoininen]

This should include info on:

• overview of what is the workflow (adding script to GitHub, adding metadata, adding data files etc)
• how to deal with data versioning (public and private versions)

[frafra]

Some previous comments/discussions providing insights on how the system works:

• Workflow: https://github.com/COATnor/COAT_portal_issues/issues/66#issue-528802223
• Production vs testing: - https://github.com/COATnor/COAT_portal_issues/issues/75#issuecomment-641851218

[frafra]

Moved to: #4