Update documentation

[andreasrosdal]

Update documentation. Making this issue so we remember.

See:

https://github.com/flyingsaucerproject/flyingsaucer/tree/gh-pages

https://flyingsaucerproject.github.io/flyingsaucer/r8/guide/users-guide-R8.html#pdf

#325 (comment)

(I might make a PR for this at some point in time.). @ivangal2

[godenji]

What would probably be most helpful to iText users (and new users in general) would be to provide even the most basic example of how to use the new API -- the README would certainly be a good start :)

Thanks for taking over the project, btw, the breakneck speed of development is impressive.