Fix doc issues

tokio/src/sync/mpsc/bounded.rs

@@ -244,7 +244,7 @@ impl<T> Receiver<T> {
  /// still outstanding [`Permits`] from before it was closed, the channel is
  /// not considered closed by `recv_many` until the permits are released.
  ///
- /// For non-zero values `limit`, this method will never return `0` unless
+ /// For non-zero values of `limit`, this method will never return `0` unless
  /// the channel has been closed and there are no remaining messages in the
  /// channel's queue. This indicates that no further values can ever
  /// be received from this `Receiver`. The channel is closed when all senders

tokio/src/sync/mpsc/unbounded.rs

@@ -179,11 +179,11 @@ impl<T> UnboundedReceiver<T> {
  /// the function returns immediately with `0`.
  /// The return value is the number of values added to `buffer`.
  ///
- /// If there are no messages in the channel's queue, but the channel has
- /// not yet been closed, this method will sleep until a message is sent or
- /// the channel is closed.
+ /// For `limit > 0`, if there are no messages in the channel's
+ /// queue, but the channel has not yet been closed, this
+ /// method will sleep until a message is sent or the channel is closed.
  ///
- /// For `limit > 0`, this method will never return `0` unless
+ /// For non-zero values of `limit`, this method will never return `0` unless
  /// the channel has been closed and there are no remaining messages
  /// in the channel's queue. This indicates that no further values can ever
  /// be received from this `Receiver`. The channel is closed when all senders