In addition to comments in your source code for developers, users may expect the follow types of documentation:
Man pages - see the “Linux Man-Page-HOWTO”
Command line accessible documentation - often accessible with the “-h” and the “--help” options.
The following files distributed with the software:
Describes basic installation, compilation, and even basic use instructions: at least 30 lines long and more no more than 250
Should be much shorter than the README file and should quickly and concisely describe how to build and install the program: rarely over 100 lines
Logs or documents the changes you make to your program
Frequently Asked Questions
Project Website (SourceForge?)