Updated readme and added new sample project

samples/ReadmeSample/Entities/Order.cs

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+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;
+    }
+}

samples/ReadmeSample/Entities/OrderItem.cs

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+namespace ReadmeSample.Entities
+{
+    public class OrderItem
+    {
+        public int OrderId { get; set; }
+        public int ProductId { get; set; }
+        public int Quantity { get; set; }
+
+        public Order Order { get; set; }
+        public Product Product { get; set; }
+    }
+}

samples/ReadmeSample/Entities/Product.cs

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+namespace ReadmeSample.Entities
+{
+    public class Product
+    {
+        public int Id { get; set; }
+
+        public string Name { get; set; }
+
+        public decimal ListPrice { get; set; }
+    }
+}

samples/ReadmeSample/Entities/User.cs

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+using System.Collections;
+using System.Collections.Generic;
+
+namespace ReadmeSample.Entities
+{
+    public class User
+    {
+        public int Id { get; set; }
+
+        public string UserName { get; set; }
+
+        public string EmailAddress { get; set; }
+
+        public ICollection<Order> Orders { get; set; }
+    }
+}