doc: fix debian version to unstable
doc: fix debian version to unstable

Looks like qtile never made it out of unstable, so let's not claim it did.

Closes #1493

Signed-off-by: Tycho Andersen <6b523322678240882acbb4da5312a12d8cd0082d@tycho.ws>

ramnes/qtile,qtile/qtile,qtile/qtile,tych0/qtile,ramnes/qtile,tych0/qtile