stream: Fix FailoverPool doc

Author: frostyplanet

stream/src/client/failover.rs

@@ -23,8 +23,9 @@ use std::sync::{
 /// Only retry RpcIntErr that less than RpcIntErr::Method,
 /// currently ignore custom error due to complexity of generic.
 ///
-/// NOTE: there's cycle reference inside FailoverPoolInner and it's ClientPool,
-/// don't clone FailoverPool as it has custom drop. FailoverPool should be put in Arc for usage.
+/// NOTE: there's cycle reference inside FailoverPoolInner and its ClientPool,
+/// FailoverPool::drop will break the cycle reference. This means we cannot impl Clone for FailoverPool,
+/// but you can put FailoverPool within Arc if you need to clone.
 pub struct FailoverPool<F, P>(Arc<FailoverPoolInner<F, P>>)
 where
     F: ClientFacts,