Everything that doesn't need to be secure is in gitlab.com. When I used github.com I started a repository that I called "etudes" which were code and explanatory notes that went into a separate wiki repository. I used etudes for notes to myself and larger multipart explanations for others. After switching to gitlab.com, which doesn't really do wikis, I amalgamated code and notes into one repository and that works better.

For more secure information that I want to be more portable I use tiddlywiki on a USB stick.

https://en.m.wikipedia.org/wiki/TiddlyWiki