Adding documentation for specifying diagrams

[reagle]

Thanks for this plugin! I'm trying to figure out how to use it and find it confusing that mermaid captions can be specified using Quarto's %%| syntax and pandoc's attribute syntax. The documentation could give a bit more guidance about the recommended means of specification.

[ppenguin]

May I add to this that I haven't yet been able to find information about specifying sizes, background color etc (in my case plantuml rendering for reveal-js (html) output.

It seems for background color only part can be specified in the diagram itself, but during svg generation it appears there is a container generated for which it is unclear how to influence the style.

That it's possible to specify size like {.plantuml width=60%} I found somewhere on the webs, but it's also not documented.