Added description of mapdisplay option

Author: Herugrim

docs/docs/how_it_works.md

@@ -111,6 +111,7 @@ Also controls True or False:
 - fullscreen_control
 - scroll_wheel
 - collapsible (map collapses by click on **varname**\_collapse button)
+- mapdisplay (show a collapsible map by default or not)
 - center_on_user_location (using HTML5 Geolocation)
 
 ### 2. Template