Improve documentation example for `DispatchManagingActor`

[llucax]

The DispatchManagingActor example in the class docs should do something else than just listening to updates.

Maybe it is worth adding some other logic to represent that, maybe implement a ClockActor that ticks every X time, where X is a dispatch option? So we have a select() instead with a timer (printing the time) and the updates_channel.

The example should also clearly show that the managed actor's _run() method should first receive from the updates channel, otherwise it might miss the initial setup of the dispatch. This should also probably be mentioned more explicitly in the docs themselves, not just the example.

I even wonder if we should somehow enforce this, requiring a special start() method for managed actors or something like that.

Originally posted by @llucax in:

• Dispatch Managing Actor #54 (comment)
• Dispatch Managing Actor #54 (comment)