doc: rename "Wayland" to "publican"

This directory was called Wayland during my early tries with publican where
the source layout was different and it needed to be set to the same name as
the publican output directory. This reason doesn't exist anymore, so re-name
it to publican to make it more obvious what's hiding in here.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>