How to Write Good Documentation
Documentation is one of the most important and under-rated aspects of any library or open-source project. If you are writing code that will be used by someone other than yourself, it needs to be documented. Period.
After using many libraries (both open-source and private), and writing a few of my own, I noticed that all good documentation can be broken down into a bunch of distinct elements.
Source: How to Write Good Documentation (And Its Essential Elements), an article by Soham Kamani.