How to set CloudWatch alarms for non-compliancy in AWS Config rules?
From what I know of AWS Config there's no way at the moment to directly publish a metric from which you can base an alarm.

If the notification has to come from a Cloudwatch alarm then AWS Config will let you execute Lambda based on rules set up in AWS Config - link.

If you want a simpler option AWS Config also lets you publish directly to an SNS topic when your rule is evaluated - link

Failing this you can also watch for CloudTrail events and then publish a CloudWatch metric which you can base an alarm on. This is fairly in depth though and if the important part is getting the emails to be looked at by a person then your best bet is probably to have AWS Config publish directly to SNS itself.