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

[MarcoRavich]

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

Since we've 'doxed' it in our HyMPS project (under AUDIO section \ AI-based page \ Transcriptings), can you please add a GH-compliant license file for it ?

As you know, expliciting licensing terms is extremely important to let anyone better/faster understand how to reuse/adapt/modify sources (and not only) in other open projects and vice-versa.

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

(badge-generator URL: https://badgen.net/github/license/thru-goes-hamilton/Guitabify)

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

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

Hope that helps/inspires !