In most common scenarios, README files can have one of the following layouts.
The basic layout might seems too much in the beginning, but I think this is quite essential and valuable information that each open source project could have.
Including these additional sections in the README almost eliminates the need to write an introductory blog post about the project.
As the project becomes bigger and successful, these additional sections tend to minimize potential duplicate questions on Stack Overflow and questions as issues on GitHub.
1 The description for the maturity levels of open source code can be found here.