this was necessary today for team#41815 so we should make sure
to remember how to handle this case.

Turns out we had a missing paren, but also it seems like just having
the en-encoded parens, *just for this link*, broke things.

Markdown parsers, go figure.

Closes: tpo/web/donate-neo#75

I've just tried this this morning and it works as expected: thunderbird
presents the list of calendars with just the missing ones selected.