Make licensing more explicit

Cargo.toml

@@ -5,7 +5,7 @@ documentation = "https://docs.rs/num-complex"
 homepage = "https://github.com/rust-num/num-complex"
 keywords = ["mathematics", "numerics"]
 categories = ["algorithms", "data-structures", "science", "no-std"]
-license = "MIT/Apache-2.0"
+license = "MIT OR Apache-2.0"
 name = "num-complex"
 repository = "https://github.com/rust-num/num-complex"
 version = "0.3.0"

README.md

@@ -38,3 +38,18 @@ Release notes are available in [RELEASES.md](RELEASES.md).
 ## Compatibility
 
 The `num-complex` crate is tested for rustc 1.31 and greater.
+
+## License
+
+Licensed under either of
+
+ * [Apache License, Version 2.0](http://www.apache.org/licenses/LICENSE-2.0)
+ * [MIT license](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.