Clarify license as OR

Author: jonhoo

README.md

@@ -206,3 +206,20 @@ the running data-flow graph. You can also deploy Noria's
 [more advanced web UI](https://github.com/mit-pdos/noria-ui) that serves
 the REST API endpoints in a human-digestible form and includes the
 graph visualization.
+
+## License
+
+Licensed under either of
+
+ * Apache License, Version 2.0
+   ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
+ * MIT license
+   ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
+
+at your option.
+
+## Contribution
+
+Unless you explicitly state otherwise, any contribution intentionally submitted
+for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
+dual licensed as above, without any additional terms or conditions.