Added Copyright Header

Reviewed By: davidaurelio

Differential Revision: D10462700

fbshipit-source-id: edef1f6f5825835bbdb613a1934bf7bfe86d0ee6

tools/build_defs/oss/yoga_defs.bzl

@@ -1,3 +1,9 @@
+#
+#  Copyright (c) Facebook, Inc. and its affiliates.
+#
+#  This source code is licensed under the MIT license found in the LICENSE
+#  file in the root directory of this source tree.
+#
 """Provides macros for working with yoga library."""
 
 YOGA_ROOTS = ["//..."]