[libvirt] [PATCH] Add link to how-to-contribute doc from HACKING file

Very trivial patch which adds a link to my document on how to contribute to open source projects to the HACKING file. http://et.redhat.com/~rjones/how-to-supply-code-to-open-source-projects/ Rich. -- Richard Jones, Emerging Technologies, Red Hat http://et.redhat.com/~rjones Read my OCaml programming blog: http://camltastic.blogspot.com/ Fedora now supports 59 OCaml packages (the OPEN alternative to F#) http://cocan.org/getting_started_with_ocaml_on_red_hat_and_fedora