"man fuse" refers to non-existent "fuse" group

[Jo Liss]

`man fuse` from package fuse 2.9.4-1ubuntu3 amd64 on Ubuntu Server Xenial (16.04) says:

    SECURITY
           The fusermount program is installed set-user-gid to fuse. This is done to allow users from fuse group to mount their
           own filesystem implementations.

I think this used to be true in 14.04, but it's no longer true in 16.04. `/bin/fusermount` is now set-uid root, and there is no `fuse` group:

    $ ls -l /bin/fusermount
    -rwsr-xr-x 1 root root 30800 Mar 11 15:43 /bin/fusermount
    $ grep fuse /etc/group
    $

I'm not sure if there *should* be a `fuse` group, or if the man page needs to be updated.