Recently I discovered the quite wonderful markdown editor Zettlr (https://www.zettlr.com/download). But it has no Solus version. Is this the appropriate place to request that the app be added to your Software Center? So far, Solus is breathing life back into my 2012 Acer laptop!
Zettlr markdown editor
All this can be found using the Docs link from the top navigation bar... I don't why nobody dares to click it 
Another option is to try one of the editors already packaged for Solus. A (possibly imcomplete) list:
- Uberwriter
- Ghostwriter
- Retext
Though not in the repo I use Marker for it's sheer simplicity https://flathub.org/apps/details/com.github.fabiocolacio.marker
Personally I'd recommend either QOwnNotes (if you need to define a hierarchical structure, you can use it without having Nextcloud set up, they're just Markdown files in folders) or Ghostwriter like @davidjharder mentioned.