Clarify licensing page
Clarify licensing page

- Say specifically how we'd like to be cited.
- Use data source names clearly.
- Reformat.

cmu-delphi/delphi-epidata,cmu-delphi/delphi-epidata,cmu-delphi/delphi-epidata,cmu-delphi/delphi-epidata,cmu-delphi/delphi-epidata,cmu-delphi/delphi-epidata