Add qpm() docs

[NeroBlackstone]

Please confirm the changes to ensure that I understand correctly

[Datseris]

Yes that is correct, the code doesn't account for tempo changes. Perhaps it should?

Do we have a function that returns

    for event in t.tracks[1].events
        if event isa SetTempoEvent
            push!(list, 6e7 / event.tempo)
        end
    end
return list

so that a user may find all tempo changes and have a list of QPM over time?

[NeroBlackstone]

Yes that is correct, the code doesn't account for tempo changes. Perhaps it should?

Do we have a function that returns

    for event in t.tracks[1].events
        if event isa SetTempoEvent
            push!(list, 6e7 / event.tempo)
        end
    end
return list

so that a user may find all tempo changes and have a list of QPM over time?

I think tempochanges() function already implemented what you said, so I think It's okay to just add the doumentation to remind users.