Update userguide to describe border styles better
Update userguide to describe border styles better

Describe the difference between normal and pixel titlebars better

Thanks to @JonWoodlief 
i3/i3,Airblader/i3-original,Airblader/i3,Airblader/i3,Airblader/i3,stapelberg/i3,Airblader/i3,stapelberg/i3,Airblader/i3-original,Airblader/i3-original,stapelberg/i3,i3/i3,Airblader/i3-original,stapelberg/i3,Airblader/i3-original,i3/i3,i3/i3