[REQ] Add a (GH-compliant) license file

[MarcoRavich]

Hi there, 1st of all thanks for this cool work !

Since we've "doxed" it in our HyMPS project (under the AUDIO category \ Engines page, can you please add a (GH-compliant) license file ?

Although it may sounds like a minor aspect, license file omission causes an inconsistent generation of the relative badge too:

(badge-generator URL: https://flat.badgen.net/github/license/VoidXH/Cavern/?label=LICENSE)

Anyway you can also easily set a "correct" one through the GH's license wizard tool.

Last but not least, let us know - in your opinion - how we could improve our categorizations and links to resources in order to favor collaboration between developers (and therefore evolution) of listed projects.

Thanks in advance.

[VoidXH]

Added in da636cf.

[MarcoRavich]

Thanks, I'll manually set the badge to "Other" (since the license it's not a standard one) then.