How to: Add new license rules for enhanced detection

ScanCode relies on license rules to detect licenses. A rule is a simple text file containing a license text or notice or mention. And a small YAML text file that tells ScanCode which licenses to report when the text is detected.

See the FAQ for a high level description of how to add a new rule.

See the #257 issue and the related #258 pull request for an example: this adds a new rule to detect a combination of MIT or GPL.