Expand text about MLs on Community page

[amoeba]

As discussed on the 2023-02-01 Arrow Community Meeting, this expands the text around tag uses on the mailing list. I tried to keep it short so let me know if there areas that would be better expanded (such as voting).

Closes apache/arrow#33989

[ianmcook]

Thanks for doing this @amoeba! I have two small suggestions:

• I think this would be better if the language about the prefixes was a bit stronger and more directive. E.g. "Please prefix the subject line" instead of "You may want to prefix the subject line"
• Could you include some illustrative examples of full subject lines including the prefix? I'm not sure everyone who reads this will immediately recognize what "prefix" means, so I think it is helpful to show full examples.

[amoeba]

Thanks for the review @ianmcook and apologies for the delay in responding. I think those are great suggestions and I took a shot at them in 0ad7a4d. This is ready for another look.

[kou]

+1