sync: update watch channel docs (#6395)

tokio/src/sync/mod.rs

@@ -278,7 +278,7 @@
 //!
 //! ## `watch` channel
 //!
-//! The [`watch` channel] supports sending **many** values from a **single**
+//! The [`watch` channel] supports sending **many** values from a **many**
 //! producer to **many** consumers. However, only the **most recent** value is
 //! stored in the channel. Consumers are notified when a new value is sent, but
 //! there is no guarantee that consumers will see **all** values.

tokio/src/sync/watch.rs

@@ -1,6 +1,6 @@
 #![cfg_attr(not(feature = "sync"), allow(dead_code, unreachable_pub))]
 
-//! A single-producer, multi-consumer channel that only retains the *last* sent
+//! A multi-producer, multi-consumer channel that only retains the *last* sent
 //! value.
 //!
 //! This channel is useful for watching for changes to a value from multiple