Include the minutes in the icalendar export

[bert-github]

An event can have a URL to minutes, but that URL is not included in the export to ICS. It would be handy if it were.

Maybe it can be added at the end of the DESCRIPTION: \n\nMinutes\n\nhttps://example.org/my-minutes; or as an ATTACH property with a made-up parameter: ATTACH;X_LABEL=minutes:https://example.org/my-minutes

[plehegar]

Doing this would help with https://github.com/w3c/calendar/issues/9 . At least, if it's in the export, we can make on the side a compact view of meeting records.