Documentation/process: update FUSE project website

According to the old project site, https://sourceforge.net/projects/fuse/
the project has moved to https://github.com/libfuse/

 so we update the
link to point to the latest libfuse release.

Signed-off-by: Martin Kepplinger <martink@posteo.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>