Include license in nuget package

[daverant]

Some licensing tools I use (Snyk) were failing to identify SharpCompress' MIT license as it's not bundled into the Nuget package. This bundles LICENSE.txt in the root of the repo into the package following guidance here.

Before:

After:

Could alternatively include an SPDX license expression but this wouldn't include specific wording for the author's copyright

<PropertyGroup>
    <PackageLicenseExpression>MIT</PackageLicenseExpression>
</PropertyGroup>

[adamhathcock]

Thanks...I had tried to do this myself but could not find the correct combination of options :(