Improve CLI documentation

Iris observations:

The "reference" part of the documentation misses examples and a clear explanation what "experiment", "dataset" (this is the metadata?), "File" are. If there is an explanation somewhere in the "Tutorials" or "getting started" maybe link it there?

For me it is totally confusing when I need to decide if "path" or "filename" should be just the filename, just the path, or the full qualified filename. Examples would be very helpful.

After these improvements send an email to Iris