add ammo can plugs pic

input/projects/quadcopters/rc_equipment.md

 lightgallery([
     [ "img/ammo_can_bat_store_1.jpg", "Outside view of cans" ],
     [ "img/ammo_can_bat_store_2.jpg", "Look inside the cans" ],
+    [ "img/ammo_can_plugs.jpg", "Close look at rubber plugs" ],
 ])
 %-->