I do not code, so take what I say in that context. I use Geany because it does many things - and a guy who won a coding competition says he uses only Geany. Geany is far lighter than Atom (which is owned now by Microsoft). Geany handles markdown fairly well and I use mostly markdown. But, plan to learn a tiny bit of code. For terminal, i use use nano or something similar called micro. Both nano and micro can open/use markdown (.md) or .txt, and, though they cannot open .rtf, if i use Ranger terminal file manager, they can show the preveiwed contents of an .rtf file, but cannot open it to edit it that way. Geany can open .rtf if it has no graphics - so text only. If there is formatting added, though, it is an ugly sight. I am testing software on a slow HDD in order to have a very light, fast system and Geany does fine on it.