Add FAQ section to improve user guidance

[AoifeHughes]

This pull request adds a new FAQ section to the Turing.jl website and updates the navigation menu to include a link to the FAQ page. The FAQ section provides answers to common questions about using Turing.jl, covering topics such as random variables, implementing samplers, parallelism, debugging, syntax differences, automatic differentiation backends, and performance issues.

Website Navigation Update:

• _quarto.yml: Added a new link to the FAQ page in the website's navigation menu.

FAQ Section Addition:

• faq/index.qmd: Created a new FAQ page with detailed answers to common questions about Turing.jl. Topics include variable treatment, sampler implementation, parallelism, type stability, debugging, syntax differences, automatic differentiation backends, and performance debugging.

Relevant Issues:

• Request: FAQ section #437
• Introduce a docs FAQ section Turing.jl#2431
• Automate choice of AD backend Turing.jl#2417
• Better performance guidelines and support for user Turing.jl#2414

[Copilot]

Pull Request Overview

This PR adds a new FAQ section to the Turing.jl website and updates the navigation menu to include a link to it.

• Added a “FAQ” entry in the site navigation
• Created faq/index.qmd with a set of common Q&A on using Turing.jl

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
_quarto.yml	Inserted a navigation entry for the FAQ
faq/index.qmd	Added FAQ page with detailed user guidance

Comments suppressed due to low confidence (1)

_quarto.yml:27

• Indentation of the new navigation entry does not match the surrounding items and could break the YAML. Align the - href: faq/ and its text: line with the other menu entries.

- href: faq/

[github-actions]

Preview the changes: https://turinglang.org/docs/pr-previews/608
Please avoid using the search feature and navigation bar in PR previews!

[penelopeysm]

This is a nice start, I think there are a few places where it's necessary to go into more detail, which I've commented on.

General comment for the entire PR: for the URLs, you can use the meta variables defined in _quarto.yml, i.e. [text]({{< meta usage-automatic-differentiation >}}) to avoid hardcoding relative paths (useful if you want to move pages around, which has happened a couple of times).

[penelopeysm]

This doesn't answer the stated question?

If it's a question about syntax, I would personally think it's best to have Turing vs Stan in a single section, and Turing vs (other PPL) can be a different section. Apart from the parameter block, two of the common things that Stan models have that Turing doesn't are transformed data and generated quantities -- the gist in Turing is that any data transformations should be done before defining the model (so it's decoupled from the model) and generated quantities are covered in https://turinglang.org/docs/usage/tracking-extra-quantities/index.html.

[penelopeysm]

I know you took the list questions from somewhere else, but I don't really like this question. I don't get the intent behind it (what is the answer supposed to be?) and the result of this is, I think, reflected in the text, which is very vague and IMO not very helpful. If the answer is basically to read the performance section.

IME interactions with AD backend don't often lead to performance differences, usually it either runs fine or it crashes. If the AD is unusually slow it usually reflects slowness in the model itself.

[AoifeHughes]

I think I've addressed the comments @penelopeysm

[penelopeysm]

Looking good! Thanks for expanding on the points here. A few more comments, which hopefully aren't too complicated to deal with.