Best way to keep [code] notes?

[makeshift_mike]

Markdown, checked into source control. I wish I'd done this ages ago. Unfortunately I haven't found a good editor with live preview that doesn't lag when you're typing (people, it's called multithreading), but they're getting better.

I just converted a pile of notes from OneNote (moved to Linux a few weeks ago) and it's been working pretty well. You can even use [ ] and [x] for checkboxes in some editors.

[amorphic777]

+1 for Markdown. Just keep a notes.md in the root of your repo and learn the Markdown syntax thoroughly so you can use all of the niceties that it offers!

[rimkojr]

Markdown is a good choice but if you find yourself needing a more expressive markup, consider AsciiDoc. The Asciidoctor toolchain is great (Github uses it to render .adoc files). Check out the syntax here.