Add advisory for data race in toolshed

crates/toolshed/RUSTSEC-0000-0000.md

@@ -0,0 +1,21 @@
+```toml
+[advisory]
+id = "RUSTSEC-0000-0000"
+package = "toolshed"
+date = "2020-11-15"
+url = "https://github.com/ratel-rust/toolshed/issues/12"
+categories = ["memory-corruption"]
+keywords = ["concurrency"]
+
+[versions]
+patched = []
+```
+
+# CopyCell lacks bounds on its Send trait allowing for data races
+
+`CopyCell<T>` is a `Cell`-like type that is implemented for any type `T` that
+is `Copy`able. It's `Send` trait has no bounds on the contained type.
+
+As not all `Copy`able types are thread safe, for example non-mutable references
+implement the `Copy` trait, it is possible to send references to types with
+interior mutability such as `Cell` across threads and cause data races.