LiveBroadcaster is a tool that will automatically post to your Twitter when you go live on Twitch.
Connect your Twitch to register, connect your Twitter and enter your going live message, simple as that!
You can use variables like "{url}" and "{title}" in your message, these will be replaced with your stream url and title when posting to Twitter.
Preview the tweet that will be sent in real-time, allowing you to see what the finished version will look like!