multicore: Documentation tweaks

Co-authored-by: Daira Hopwood <daira@jacaranda.org>

CHANGELOG.md

@@ -9,7 +9,8 @@ and this project adheres to Rust's notion of
 ### Added
 - `BELLMAN_NUM_CPUS` environment variable, which can be used to control the
   number of logical CPUs that `bellman` will use when the (default) `multicore`
-  feature flag is enabled.
+  feature flag is enabled. The default (which has not changed) is to use the
+  `num_cpus` crate to determine the number of logical CPUs.
 - `bellman::multicore::Waiter`
 
 ### Changed

src/multicore.rs

@@ -114,7 +114,7 @@ mod implementation {
             self.receiver.recv().unwrap()
         }
 
-        /// One off sending.
+        /// One-off sending.
         pub fn done(val: T) -> Self {
             let (sender, receiver) = bounded(1);
             sender.send(val).unwrap();
@@ -185,10 +185,10 @@ mod implementation {
     impl<T> Waiter<T> {
         /// Wait for the result.
         pub fn wait(&mut self) -> T {
-            self.val.take().unwrap()
+            self.val.take().expect("unmet data dependency")
         }
 
-        /// One off sending.
+        /// One-off sending.
         pub fn done(val: T) -> Self {
             Waiter { val: Some(val) }
         }