Add license to the NuGet package

[Scal-Human]

Hi,

I am currently automating the generation of Citation.cff files for a bunch of projects in order to:

• attribute the work to the appropriate person (that is you ;-) by having references under my own attribution
• validate the compatibility of the projects' license against the components it uses.
  This process is based on the content of the packages used by the project, and I mention that your Nuget package have a license expression "License".
  It would be IMHO a good idea, to update it to "MIT" on future versions.

Thank you for you work,
Scal