        "refresh":
        {
            "text" : "",
            "posX" : 25,
            "posY" : 35,
            "alignment" : "left_center",
            "width" : 20,
            "height" : 20,
            "hoverSound" : "modpack:buttonsound.wav",
            "texture" : "custommainmenu:textures/gui/buttons.png",
            "action" : 
            {
                "type" : "refresh"
            }
        }
	},

If you want the reload button for the main menu add this in under the "mods" tag if you want to be able to use it. 
You need to restart your game once you've added the reload button and saved the file.