License field

[Faré]

I propose we document that the license field should if possible
contain an identifier from
  http://spdx.org/licenses/
  http://esr.ibiblio.org/?p=6867

—♯ƒ • François-René ÐVB Rideau •Reflection&Cybernethics• http://fare.tunes.org
You think you know when you can learn, are more sure when you can write,
even more when you can teach, but certain when you can program.
        — Alan Perlis