Since Raw post button is such a hit, see the hearts, in the same light here is another problem that as a site admin I am constantly writing a reply to users to explain how to use Markdown.
As I have never written a theme or plugin yet I don’t know which one would be needed to solve this problem but hope it is a theme.
When editing a post, in the tool bar should be a ? icon or something that takes one either to a page that explains Markdown on the site, or a popup that shows the Markdown.
You mean that you simply want to add another button to the composer which opens an external webpage (with a Markdown tutorial)?
That would work also.
Since I did not know what the exact meaning of composer I looked for uses of the word here and found Do we need a help button on the composer?.
As our site is on the standard plan as Open Source Project we are not allowed to install this or any plugin.
But for this specific idea, only the Markdown and BBCodes are needed to be noted in a popup, or if linking to a page, with demonstrative examples.