Document font update pitfall
Document font update pitfall

If a font file associated to a font used by Qtile is updated, Qtile
may crash.  The resulting logs might be somewhat confusing.  This commit
documents this pitfall in three places, including the default Qtile
configuration file so that users are aware of it and can avoid it.

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