Add shell completions by shtab

[Freed-Wu]

vimdoc --print-completion bash | sudo tee /usr/share/bash-completion/completions/vimdoc
vimdoc --print-completion tcsh | sudo tee /etc/profile.d/vimdoc.completion.csh
vimdoc --print-completion zsh | sudo tee /usr/share/zsh/site-functions/_vimdoc

❯ vimdoc -<TAB>
option
--help               show this help message and exit
-h                   show this help message and exit
--print-completion   print shell completion script
--version            show program's version number and exit
❯ vimdoc <TAB>
plugin
scripts/  tests/    vimdoc/

    extras_require={'completion': ['shtab']},

[dbarnett]

@Freed-Wu do you know if it gives self-contained usage details for how to set up the completions that you can access from vimdoc --help or something? Otherwise we might want to add a note to README or something.

[Freed-Wu]

how to set up the completions

The setup method can be seen from https://docs.iterative.ai/shtab/use/. Maybe a note is useful.