How do I add my script to the "Assets/Create" menu?

Hey, I want to add my script (an Item-script with name, ID and image) to the menu at "Assets/Create". I can display it when I right-click, but I want to know, how to add a new instance of this class to the files when I click on it, just like you do with materials and C# scripts. How do I do this?

The script looks like this:

 using UnityEngine;
 using System.Collections;
 using UnityEditor;
 
 public class Item {
     public Sprite itemImage;
     public string itemName;
     public string itemID;
 
     public Item(Sprite image,string name, string ID) {
         itemImage = image;
         itemName = name;
         itemID = ID;
     }
 }