Sammy Kaye Powers wrote a post on how to contribute to the PHP documentation.

If you've been wanting to contribute to PHP internals, starting with the documentation can be a great entry point; especially because it doesn't require dusting off those old C books from college. But knowing where to start can be tricky since information on how to contribute to the docs is scattered across the internet.

Phew! After reading this process my intentions of contributing melted away like snow in the sun. Editing the documentation should be much easier.  I believe there would be more contributions if the docs would reside in a git-repo as markdown-files.