A CLAUDE.md with vague notes is useless, because concrete details are what make it work.
Include your build commands (npm run dev, make test), your directory layout, your primary frameworks, and how to run the test suite. If your project has non-obvious architecture decisions, explain them.
I'll be direct: run /init in any project to have Claude generate a starter file by reading your codebase. Then edit it and add the things Claude got wrong or missed. The more specific you are, the less you'll need to repeat yourself.