Review cmdstanr approach to documentation and implement good ideas here

[seabbs]

Is your feature request related to a problem? Please describe.
cmdstanr has some really nicely organised pkgdown documentation and I think we could learn a lot from them. In the first instance I think this issue could be a good place to track what we like and serve as a launching point for improving our documentation

Describe the solution you'd like

• Discussion in this issue about what we like in the cmdstanr docs.
• An agreed list of features we would like to implement in our docs (if any)
• These features to be implemented.
• Notes on these features to be added to the wider epinowcast org docs so that we can standardise across packages.

Describe alternatives you've considered
No action being taken as we are happy where we are.

Additional context

cmdstanr docs here: https://github.com/stan-dev/cmdstanr

[seabbs]

I like how they have made use of the articles feature to organise their vignettes and direct people to the automatically generated package reference page at the top of their function reference. I also really like the sparsity of text they have in their readme that quickly directs to vignettes and summarises their goals - we now have a very nice README so perhaps more change their is not needed?