Offer a way to help format supplementary part

[cderv]

https://github.com/quarto-journals/plos/blob/1f79ef691a0538a94eaedd1b3c8488e5fc3e7008/style-guide/plos_latex_template.tex#L320-L345

[cderv]

It will be like this

::: {.supp}
## S1 Fig. {#s1-fig}

Bold the title sentence will be the first paragraph

Add descriptive text after the title of the item (optional) as second paragraph
:::

to produce

 \paragraph*{S1 Fig.} 
 \label{s1-fig} 
 {\textbf Bold the title sentence.} Add descriptive text after the title of the item (optional). 

in LaTeX

This will allow formating in HTML later.