doc: publican: Set table of contents depth to 1
doc: publican: Set table of contents depth to 1

This way looks more pretty, in particular for the Appendix which spawns a big
subsections chain.

Signed-off-by: Tiago Vignatti <f080760b2054d506aacc8dee97f8804c19fbc3aa@intel.com>

mchalupa/wayland,bitfactor/wayland,bitfactor/wayland,abooij/wayland,sir-murray/wayland,abooij/wayland,tulcod/wayland,eyolfson/wayland,sir-murray/wayland,mchalupa/wayland,tulcod/wayland,sir-murray/wayland,tulcod/wayland,eyolfson/wayland,abooij/wayland,mchalupa/wayland,bitfactor/wayland,eyolfson/wayland