feat: nargo command to generate shell completions

[asterite]

Description

Problem

Resolves #6284

Summary

Additional Context

I copied the command name, and learned how to install shell completions, by reading this: https://apple.github.io/swift-argument-parser/documentation/argumentparser/installingcompletionscripts/

I don't know how we can teach users to install completions... maybe some know... for those who don't, maybe they stumble upon the above page. Or should we document this in our documentation? Or in the command itself? (maybe too long)

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[aakoshh]

Nice! It could be hinted at in the output of noirup; similar installers mention zsh and fish env vars and path settings.

https://noir-lang.org/docs/reference/nargo_commands could be another good place to mention it. (This might be generated automatically by codegen_nargo_reference.sh 💪 )

[asterite]

Oh, it seems that nargo_commands page is automatically generated from the doc comments... so to change it we'd have to also add those comments to the command and to its output, which is maybe not good.

Maybe this can go without docs... people wanting to install shell completions probably know how to install them.

[aakoshh]

Yes, I realised that to include any hint in the reference would go against you trying to keep it from the command docs. Perhaps it's worth mentioning under https://github.com/noir-lang/noir/blob/master/docs/docs/getting_started/quick_start.md#nargo instead?

[TomAFrench]

I think that having a small page in the docs which explains where to place the generated completion script would be nice but not a hard requirement for this.

[asterite]

Around the "Quick start" section sounds good to me. I don't know if on that page, though, because it's more about using some nargo commands.

Maybe it could be a new "Nargo shell completions" subsection here?

[aakoshh]

There is also https://github.com/noir-lang/noir/blob/master/docs/docs/getting_started/noir_installation.md but it doesn’t mention nargo, so I thought the other one is a nicer place to make people aware of this goodie

[asterite]

I added some docs. I created a new page under "Getting started" for it, then linked it from the "Quick start" and "Standalone Noir Installation" pages. I guess it makes sense that it's a bit more prominent than what I initially thought as it could be very helpful to have those completions.

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🚀 Deployed on https://6724e1e06efe6516c682b4e4--noir-docs.netlify.app

[github-actions]

FYI @noir-lang/developerrelations on Noir doc changes.