Update the documentation
Update the documentation

Mention the possibility to use pango markup in the text tag.

xfce-mirror/xfce4-genmon-plugin,dnschneid/xfce4-genmon-plugin,tonypaulic/xfce4-genmon-plugin,tonypaulic/xfce4-genmon-plugin,xfce-mirror/xfce4-genmon-plugin,tonypaulic/xfce4-genmon-plugin,xfce-mirror/xfce4-genmon-plugin,dnschneid/xfce4-genmon-plugin,dnschneid/xfce4-genmon-plugin