Add NOTICE file to this repo (#6)

diff --git a/NOTICE.md b/NOTICE.md
new file mode 100644
index 0000000..511e1fd
--- /dev/null
+++ b/NOTICE.md
@@ -0,0 +1,5 @@
+Apache OpenWhisk Runtime PHP
+Copyright 2016-2018 The Apache Software Foundation
+
+This product includes software developed at
+The Apache Software Foundation (http://www.apache.org/).