Nuget package license enhancement

[Greybird]

Hi,

Currently, the nuget license references the master branch document: https://github.com/twilio/twilio-csharp/blob/HEAD/LICENSE
As such it creates a moving reference to the licence, even for old packages.

Would it be possible to switch to license expressions, or, if not possible to have an immutable link for the license of the package ?

Thanks,