Add note on how to open documentation

README.md

@@ -3,4 +3,4 @@
 An implementation of the [Paillier cryptosystem](https://en.wikipedia.org/wiki/Paillier_cryptosystem) based on the Wikipedia article, to investigate simple homomorphic cryptosystems.
 This library was a research project and is not optimized nor meant for production usage.
 
-Usage can be seen in the [tests](./tests/encryption_tests.rs)
+Usage can be seen in the [tests](./tests/encryption_tests.rs) or see the (simple) documentation with `cargo doc --open`.