core/cli: add completion for hpi command

misc/completion/README.md

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+To enable completion for the `hpi` command:
+
+If you don't want to use the files here, you can do this when you launch your shell like:
+
+```bash
+eval "$(_HPI_COMPLETE=bash_source hpi)"  # in ~/.bashrc
+eval "$(_HPI_COMPLETE=zsh_source hpi)"  # in ~/.zshrc
+eval "$(_HPI_COMPLETE=fish_source hpi)"  # in ~/.config/fish/config.fish
+```
+
+That is slightly slower since its generating the completion code on the fly -- see [click docs](https://click.palletsprojects.com/en/8.0.x/shell-completion/?highlight=completion#enabling-completion) for more info
+
+To use the completions here:
+
+### bash
+
+Put `source /path/to/bash/_hpi` in your `~/.bashrc`
+
+### zsh
+
+You can either source the file:
+
+`source /path/to/zsh/_hpi`
+
+..or add the directory to your `fpath` to load it lazily:
+
+`fpath=("/path/to/zsh/" "${fpath[@]}")` (Note: the directory, not the script `_hpi`)
+
+If your zsh configuration doesn't automatically run `compinit`, after modifying your `fpath` you should:
+
+`autoload -Uz compinit && compinit`
+
+### fish
+
+`cp ./fish/hpi.fish ~/.config/fish/completions/`, an then restart your shell