Document single remote use with multi mode example

[laurensvalk]

I would like more remotes than I have hubs. I've looked around for answers but nothing seems to say exactly whether you can.

Originally posted by @ReubenH12 in https://github.com/pybricks/support/discussions/1424

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We should clarify in the documentation that only one remote can be used, but that you can add some logic to "switch modes" to add more functions to each button.