docs: include linuxcnc.1 in the manpage index and pdf
docs: include linuxcnc.1 in the manpage index and pdf

This manpage got dropped from the index a good long while ago, this adds
it back in.  (The manpage was always included in the .deb, just not in
the html and pdf index.)

Signed-off-by: Sebastian Kuzminsky <62d754cc350e84d3b1c32ae79f976f5348e74a40@highlab.com>

bmwiedemann/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,ikcalB/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,ikcalB/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,ikcalB/linuxcnc-mirror,ikcalB/linuxcnc-mirror,ikcalB/linuxcnc-mirror,ikcalB/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,ikcalB/linuxcnc-mirror