Update 4. Add auth features.md (#84)

Author: natemcmaster

docs/4. Add auth features.md

@@ -212,6 +212,8 @@ In this module we're going to add the capability for users to register and sign-
     {
         // Set as admin user
         user.IsAdmin = true;
+        // In the event user creation fails in the next few lines, set this so the admin key box still shows up on the retry page
+        AllowAdminCreation = true;
     }
 
     var result = await _userManager.CreateAsync(user, Input.Password);