custom 3d menu to append objects in blender

bl_info = {
"name": "yellowsubmarine",
"author": "anonb",
"version": (1, 0, 0),
"blender": (2, 65, 0),
"location": "Add > Mesh",
"description": "Create yellowsubmarine primitive.",
"warning": "",
"wiki_url": "",
"tracker_url": "",
"category": "Add Mesh"}


if "bpy" in locals():
       import imp


import bpy
import bmesh
import math
from mathutils import *


class OBJECT_OT_addSubmarine(bpy.types.Operator):
    '''
    Class representing an operator for adding a yellow submarine
    '''
    bl_idname = "addSubmarineButton" #name used to refer to this operator
    bl_label = "Add Submarine" #operator's label
    bl_options = {'REGISTER', 'UNDO'}
    bl_description = "Add a yellow submarine" #tooltip

    def execute(self, context):
        '''
        Function to process a click on the "Add Submarine" button
        '''
        bpy.ops.wm.link_append(directory="C:/Users/Youuser/Desktop/test_append/yellowsubmarine.blend/Scene/",
            filename="Submarine", link=False) #append submarine from .blend file
        return{'FINISHED'}


def menu_func(self, context):
    self.layout.operator("addSubmarineButton")

def register():
   # bpy.utils.register_module(__name__)
   # this adds your menu to shift-a add menu
   bpy.types.INFO_MT_add.prepend(menu_func)

def unregister():
    # bpy.utils.unregister_module(__name__)
    bpy.types.INFO_MT_add.remove(menu_func)

if __name__ == "__main__":
    register()