feat(vim): re-automate installation of pynvim
feat(vim): re-automate installation of pynvim

I used to have this automated back when it was called "neovim" (see
957af8f8f36581a1f58911177af602c), but since moving to Fig I have been
doing it manually (necessary for pretty much anything to work when you
first jump into Neovim... otherwise basically every key-press ends up
producing an UltiSnips error).

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