Add nuspec template file

[FraserGreenroyd]

Fixes #464

[FraserGreenroyd]

@BHoMBot this is a DevOps instruction. I am requesting neutral checks on: code-compliance, copyright-compliance, core, documentation-compliance, installer, project-compliance, ready-to-merge, serialisation, versioning, dataset-compliance, unit-tests

[FraserGreenroyd]

@BHoMBot this is a DevOps instruction. I am requesting neutral checks on: null-handling

[bhombot-ci[bot]]

@FraserGreenroyd I have provided neutral checks to the checks requested. These checks will need to be run properly to obtain full results.

[bhombot-ci[bot]]

@FraserGreenroyd I have provided neutral checks to the checks requested. These checks will need to be run properly to obtain full results.