Document using OneForOne with BackoffSupervisor

I remember finding this API oddly specific at first, and it came up again in

akka-actor/src/main/scala/akka/pattern/BackoffOptions.scala

@@ -166,7 +166,8 @@ trait BackoffOptions {
    * Returns a new BackoffOptions with the supervisorStrategy.
    * @param supervisorStrategy the supervisorStrategy that the back-off supervisor will use.
    *   The default supervisor strategy is used as fallback if the specified supervisorStrategy (its decider)
-   *   does not explicitly handle an exception.
+   *   does not explicitly handle an exception. As the BackoffSupervisor creates a separate actor to handle the
+   *   backoff process, only a [[OneForOneStrategy]] makes sense here.
    */
   def withSupervisorStrategy(supervisorStrategy: OneForOneStrategy): BackoffOptions
 

akka-actor/src/main/scala/akka/pattern/BackoffSupervisor.scala

@@ -65,7 +65,8 @@ object BackoffSupervisor {
    *   random delay based on this factor is added, e.g. `0.2` adds up to `20%` delay.
    *   In order to skip this additional delay pass in `0`.
    * @param strategy the supervision strategy to use for handling exceptions
-   *   in the child
+   *   in the child. As the BackoffSupervisor creates a separate actor to handle the
+   *   backoff process, only a [[OneForOneStrategy]] makes sense here.
    */
   def propsWithSupervisorStrategy(
     childProps:   Props,