Prior to this change, the udev rules were fixed to allow read-write
access only to the `plugdev` group. However, while this is the default
group for USB input devices on Debian and its derivatives, this is not
true for some systems such as openSUSE, which use `input` as the group.
This change adds a `--with-input-group` argument to `configure`, which
defaults to `plugdev`. This change also updates the install
documentation to reflect the new options.
