1. Everything that could have a README file in it, should have a README file in it.
  2. The only allowed exception is that a README in some higher level directory sufficiently explains the contents of a sub-directory.
  3. If you didn’t write a README file before creating the directory, write the README after creating it. And in particular, write it before you forget what it is and before you are gone.

README files are awesome. I even remember seeing README files names as "Readme.1st" in the MS-DOS days which had a certain sense of urgency.