add comments for users [#145]

Disco.Models/Repository/Device/DeviceComment.cs

@@ -0,0 +1,25 @@
+using System;
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Disco.Models.Repository
+{
+    public class DeviceComment
+    {
+        [Key]
+        public int Id { get; set; }
+        public string DeviceSerialNumber { get; set; }
+
+        [Required]
+        public string TechUserId { get; set; }
+        public DateTime Timestamp { get; set; }
+        [Required]
+        public string Comments { get; set; }
+        
+        [ForeignKey(nameof(DeviceSerialNumber))]
+        public Device Device { get; set; }
+        
+        [ForeignKey(nameof(TechUserId))]
+        public User TechUser { get; set; }
+    }
+}