Checkout the bot here!
You can use /upcoming to list upcoming contests, and the bot will also remind you 1 day and 1 hour before each contest (this can be enabled and disabled using /start and /stop)
Now you can add you Codeforces handles and get notifications for rating changes in CF rounds. Use /help_handles to get info on how to add handles.
The code is available on GitHub. Send us your pull requests!
Any comments and bug-reports are appreciated :)