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

[MarcoRavich]

Hi there,
as you certainly know, expliciting licensing terms is extremely important for open (documentation/listings too) projects.

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

(badge-generator URL: https://badgen.net/github/license/webprofusion/OpenAudio)

You can easily set a compliant one through the GH's license wizard tool.

Thanks in advance !

[webprofusion-chrisc]

Good point! CC-0 license applied now.