Add cake-addin tag to Cake.Services NuGet package

[augustoproiete]

The NuGet Gallery will soon include 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 will look similar to this:

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

[SharpeRAD]

Thanks, i've added the nuget tag to v1.0.1