docs(readme): Call out licenses

Author: epage

README.md

@@ -8,4 +8,13 @@
 
 ![Screenshot](./examples/expected_type.svg)
 
+## License
+
+Licensed under either of
+
+* Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or <https://www.apache.org/licenses/LICENSE-2.0>)
+* MIT license ([LICENSE-MIT](LICENSE-MIT) or <https://opensource.org/license/mit>)
+
+at your option.
+
 [Documentation]: https://docs.rs/annotate-snippets/