Improve expiry doc

src/persevero.gleam

@@ -138,6 +138,13 @@ pub type Mode {
   MaxAttempts(Int)
 
   /// Specifies the maximum duration to make attempts for.
+  ///
+  /// Note that `Expiry` mode does not stop the current wait time from being
+  /// executed. For example, if you're under the expiry timeout by 1s and your
+  /// next wait time is 10s, the next wait time, and the operation, will still
+  /// be executed, resulting in spillover. Also note that the duration of the
+  /// operation is taken into account when calculating the total duration
+  /// elapsed.
   Expiry(Int)
 }