Just noticed that pandoc is able to convert between document formats.
For example, from markdown to html:
pandoc -f gfm README.md -o README.html
and the result is quite good. This is useful for the markdown documents at
Github (format gfm) which is the format we already have.
Html could be a nice format because the generated files are quite small. Thus they could be used both online and offline. And it supports pictures.