Add copywrite headers to css files

Reviewed By: danielbuechele

Differential Revision: D6976529

fbshipit-source-id: 7f0c3fdd70105cbe055fa49f10eac3bdaf84b5c2

website/src/templates/index.css

@@ -1,4 +1,13 @@
-.doc-block.playground {
+/**
+ * Copyright (c) 2014-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+ .doc-block.playground {
   height: 1vh;
 }