Add parking_lot README

Author: sarsko

wrappers/parking_lot/README.md

@@ -0,0 +1,23 @@
+# Shuttle support for `parking_lot`
+
+This folder contains the implementation and wrapper that enables testing of [parking_lot](https://crates.io/crates/parking_lot) applications with Shuttle.
+
+## How to use
+
+To use it, add the following in your Cargo.toml:
+
+```
+[features]
+shuttle = [
+   "parking_lot/shuttle",
+]
+
+[dependencies]
+parking_lot = { package = "shuttle-parking_lot", version = "VERSION_NUMBER" }
+```
+
+The code will then behave as before when the `shuttle` feature flag is not provided, and will run with Shuttle-compatible primitives when the `shuttle` feature flag is provided.
+
+## Limitations
+
+Shuttle's parking_lot functionality is currently limited to a subset of the `Mutex` and `RwLock` primitives. If your project needs functionality which is not currently supported, please file an issue or, better yet, open a PR to contribute the functionality.

wrappers/parking_lot/parking_lot_impl/src/rwlock.rs

@@ -38,6 +38,9 @@ impl<T> RwLock<T> {
             sem,
             inner: UnsafeCell::new(value),
         };
+
+        trace!("initialized parking_lot RwLock {:p}", &rwlock);
+
         rwlock
     }
 }