Proper way to install 3rd-party library/plugin dependency?

What is the proper way to install a 3rd-party plugin, like GoKit (GitHub - prime31/GoKit: Lightweight tween library for Unity)?

Obviously, I can download it via git or a zip file or whatever, then copy the files into Assets/Plugins/GoKit, but that doesn’t feel very clean. I’m used to doing somethi…ng like “composer install …” or “yarn install …” or “npm install …”, and we have a manifest.json and a packages-lock.json, so I feel like I’m missing something pretty basic.

Tanks.

Neither their README nor their Wiki seem to include any installation instructions so I think you’re stuck with copying files from their git repo into your project.