feat: Add license header to Document

Author: HomelessDinosaur

Nitric.Sdk/Document/Document.cs

@@ -1,4 +1,16 @@
-using System;
+// Copyright 2021, Nitric Technologies Pty Ltd.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
 using System.Collections.Generic;
 namespace Nitric.Api.Document
 {