I use Boostnote[0] (not affiliated, just a happy user), it's a simple to use note keeping application that supports Markdown.
Keeping an (almost) daily journal of stuff that hangs me up has helped me immensely. You know the type of problems that take 12 hours of debugging just to find out it's something trivial? Write that down, it's sure to come up in the future and our memory isn't great at all.