Updated throttle fn comments.

Co-Authored-By: Yoshua Wuyts <yoshuawuyts+github@gmail.com>

src/stream/stream/mod.rs

@@ -318,6 +318,7 @@ extension_trait! {
         #[doc = r#"
             Limit the amount of items yielded per timeslice in a stream.
 
+This stream does not drop any items, but will only limit the rate at which items pass through.
             # Examples
             ```ignore
             # fn main() { async_std::task::block_on(async {