add apache license

Author: RichardGe

license.txt

@@ -1,4 +1,20 @@
 
+Copyright 2019 Advanced Micro Devices, Inc.
+
+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.
+
+--------------------
+
 Third Party Licenses
 
 LibTiff - tiff images - BSD license https://en.wikipedia.org/wiki/Libtiff