Rollup merge of rust-lang#149236 - tisonkun:patch-1, r=tgross35

Clarify edge cases for Barrier::new

... since n-1 is undefined when the usize n is 0.

Author: matthiaskrgr

std/src/sync/barrier.rs

@@ -65,8 +65,8 @@ impl fmt::Debug for Barrier {
 impl Barrier {
     /// Creates a new barrier that can block a given number of threads.
     ///
-    /// A barrier will block `n`-1 threads which call [`wait()`] and then wake
-    /// up all threads at once when the `n`th thread calls [`wait()`].
+    /// A barrier will block all threads which call [`wait()`] until the `n`th thread calls [`wait()`],
+    /// and then wake up all threads at once.
     ///
     /// [`wait()`]: Barrier::wait
     ///