Add example of server and client validation for React

samples/react/ReactGrid/Controllers/PeopleApiController.cs

@@ -0,0 +1,30 @@
+using System.ComponentModel.DataAnnotations;
+using System.Threading.Tasks;
+using Microsoft.AspNet.Mvc;
+
+namespace ReactExample.Controllers
+{
+    public class PeopleApiController : Controller
+    {
+        [HttpPut("api/people/{personId:int}")]
+        public async Task<ActionResult> UpdatePerson([FromBody] PersonDto person)
+        {
+            if (!ModelState.IsValid) {
+                return HttpBadRequest(ModelState);
+            } else {
+                return new HttpOkResult();
+            }
+        }
+    }
+    
+    public class PersonDto {
+        public string name { get; set; }
+        public string city { get; set; }
+        public string state { get; set; }
+        public string country { get; set; }
+        public string company { get; set; }
+        
+        [Range(1, 10)]
+        public int favoriteNumber { get; set; }
+    }
+}