clarify data structure example in mailroom tutorial

[natasha-aleksandrova]

had one student confused what the donations list represented since the values matched exactly to the already generated report table data.

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changed to random values and added some clarifying text.

[PythonCHB]

Thanks.

BTW, for small changes like this, feel free to merge yourself.

Which reminds me -- we really should figure out how to get the docs to build themselves iwth gitHub Actions -- it's not hard, I just need to get around to doing it!

[natasha-aleksandrova]

sounds good -- i'm just now sure how to publish the docs and this way you have visibility into the change for the build.