discord-vc-notification

Authorise the bot from the following URL.

https://discordapp.com/oauth2/authorize?client_id=418329413860458496&scope=bot&permissions=53484608

Then add a line to the topic of the channel you want notifications:

vc-notification: [CHANNEL]

Specify a space-delimited list of channel names to monitor.

Example

vc-notification: General

When someone joins the Voice Channel General, the bot posts a message to the text channel.

You can add "first" keyword like vc-notification: General first to suppress notifications when anyone is in the channel already.