Update IS-12 Readme

Development/third_party/is-12/README.md

@@ -1 +1,9 @@
-This directory is for JSON Schemas
+# AMWA IS-12 NMOS Control & Monitoring Protocol Specification
+
+This directory contains files from the [AMWA NMOS Control & Monitoring Protocol](https://github.com/AMWA-TV/is-12), in particular tagged versions of the JSON schemas used by the API specifications.
+
+Original source code:
+
+- (c) AMWA 2018
+- Licensed under the Apache License, Version 2.0; http://www.apache.org/licenses/LICENSE-2.0
+