On github, virtually all projects provide a README.md file (the “.md” denotes the file as type ‘Markdown’). Markdown is a means to easily style text without having to use real HTML tags – style indication is provided by the use of ASCII characters.
For instance, if you wanted to create a level 1 header (really big), simple prepend the line with ‘#’:
#My Really Big Headline
Markdown was created by John Gruber (of Daring Fireball fame): http://daringfireball.net/projects/markdown/syntax. I use to follow DaringFireball, but stopped when John started turning it into a forum for his political opinions.
Github lets you embed images in our READMEs when you use Markdown, and thus you can possible users with screen shots of what your code does.
Also, I found a free text editor, LightPaper, that lets you write using Markdown in the left pane, and shows you the rendering in a right pane: http://clockworkengine.com/lightpaper-mac/. It doesn’t show images, but it’s really nice to see in real time what the README will look at in a web browser.