README section to specify enabling no_std

README.md

@@ -40,6 +40,14 @@ let password_hash = default::pbkdf2(password).unwrap();
 assert!(default::pbkdf2_verify(&password_hash, password).unwrap());
 ```
 
+### Enabling `no_std`
+To use orion in a `no_std` context, you need to specify the dependency as such:
+
+`orion = { version = "*", default-features = false }`
+
+Note that this means you will not have access to the `default` API.
+This is because the `default` API depends on the `OsRng`, which in turn depends on `std`.
+
 
 ### Documentation
 Can be viewed [here](https://docs.rs/orion) or built with: