Add cake-addin tag to Cake.Homebrew NuGet package

The [NuGet Gallery](https://nuget.org) now includes a "Cake" tab with instructions on how to use NuGet packages in Cake build scripts. I'd like to suggest that you include the tag `cake-addin` in the NuGet package of this addin, so that the NuGet Gallery can display the correct instructions to install this addin.

The UI looks similar to this:


Documentation on best practices on tags for Cake addins: https://cakebuild.net/docs/extending/addins/best-practices#tags

Inspect the Cake.Homebrew NuGet package metadata and the project entry point that defines its package tags. Follow the linked Cake addin tagging guidance, add the requested cake-addin tag, and verify that the generated package metadata contains it.

Written by the indexing model from the issue text.