docs: Add vignette with sample instructions for GitHub Copilot.

[jakubnowicki]

Basic vignette for using LLM tools with Rhino.

How to test?

Run pkgdown::build_site() to preview the documentation page.

[pstorozenko]

Looks good. My only concern is that the UX of adding instructions to your project is suboptimal, hence I added link to documentation with markdown file as suggestion. We could consider adding function rhino::setup_llm_instructions({curosor|copilot}) in the future rhino version.

[jakubnowicki]

Looks good. My only concern is that the UX of adding instructions to your project is suboptimal, hence I added link to documentation with markdown file as suggestion. We could consider adding function rhino::setup_llm_instructions({curosor|copilot}) in the future rhino version.

Thanks for those changes. Yes, function(s) for adding instructions are something I would like in the future, once we have a more ready version of those.