Updated readme and added new sample project

samples/ReadmeSample/Entities/Order.cs

@@ -0,0 +1,25 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using EntityFrameworkCore.Projections;
+
+namespace ReadmeSample.Entities
+{
+    public class Order
+    {
+        public int Id { get; set; }
+        public int UserId { get; set; }
+        public DateTime CreatedDate { get; set; }
+
+        public decimal TaxRate { get; set; }
+
+        public User User { get; set; }
+        public ICollection<OrderItem> Items { get; set; }
+
+        [Projectable] public decimal Subtotal => Items.Sum(item => item.Product.ListPrice * item.Quantity);
+        [Projectable] public decimal Tax => Subtotal * TaxRate;
+        [Projectable] public decimal GrandTotal => Subtotal + Tax;
+    }
+}