Merge pull request #787 from polyadic/readme-licensing

Mention dual licensing in readme

README.md

@@ -111,11 +111,24 @@ MoreLinq provides more extension functions on `IEnumerable`, but has no addition
 * [Functional.Maybe](https://github.com/AndreyTsvetkov/Functional.Maybe)
 * [Tango](https://github.com/gabrielschade/tango)
 
-## Contributing
+## 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
 Contributions are more than welcome. Just open a PR :)
 If you want something easy to work on, there are a few issues marked with [good first issue].
 
+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.
+
 ### Documentation
 
 To build the documentation you need [mdBook] installed.