Make the text output of reuse lint more helpful

[carmenbianca]

Maybe provide links to FAQ/spec.

Maybe one recommendation for each bullet point if said bullet point fails?

• Bad licenses:
• Deprecated licenses:
• Licenses without file extension:
• Missing licenses:
• Unused licenses:
• Used licenses:
• Read errors:
• Files with copyright information:
• Files with license information:

[mxmehl]

Good idea. Perhaps a collected list of todo items, if one or multiple of these errors appear?