I also started doing something similar via org-files, git, emacs, and Working Copy. It has worked pretty well, though Working Copy (the iOS git client) was buggier than I expected (but they have a great developer and support). My network isn't very good, or I'd just use emacs on iOS via SSH via Blink.
That folder is just a collection of markdown files for each program / system and when I save on one device it updates the documentation on them all.
I use Atom to view and edit them on my Linux machines and a markdown editor app on my phone. This allows me to search across the notes too.
I've had this fairly simple, free, open source setup for years with no problems.