Indicate how to vote

[Dubidubiduu]

Add something like "Type /vote and the number of your option, e.x. /vote 99 for option 99", so I don't have to explain how to vote by myself.

German translation would be "Gebe /vote und die Nummer deiner Wahl ein. Ein Beispiel: /vote 99 für die Option 99"

[nickvergessen]

Are we not doing that already since the last version?

[nickvergessen]

https://github.com/nickv-nextcloud/talk_simple_poll#vote-on-a-poll-or-change-your-mind Maybe it could be explanded a bit. Feel free to shoot in a PR