Create a bot, gets its API token, get the ID of the channel.
https://core.telegram.org/bots/api#sendmessage
$ curl -X POST \
-H 'Content-Type: application/json' \
-d '{"chat_id": "541123411", "text": "This is a test from curl", "disable_notification": true}' \
https://api.telegram.org/bot$TELEGRAM_BOT_TOKEN/sendMessage