Update changelog

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ### Removed
 
+ * `PyToken` was removed due to unsoundness (See [#94](https://github.com/PyO3/pyo3/issues/94)).
  * Removed the unnecessary type parameter from `PyObjectAlloc`
 
 ## [0.5.0] - 2018-11-11

src/instance.rs

@@ -16,6 +16,9 @@ use crate::typeob::{PyTypeInfo, PyTypeObject};
 use crate::types::PyObjectRef;
 
 /// Any instance that is managed Python can have access to `gil`.
+///
+/// Originally, this was given to all classes with a `PyToken` field, but since `PyToken` was
+/// removed this is only given to native types.
 pub trait PyObjectWithGIL: Sized {
     fn py(&self) -> Python;
 }