Step 1: Go to http://maps.google.com/
Step 2: Search for your business listing
Step 3: Click on your business listing>>Edit>> Under the HOMEPAGE section, you can add the link of your Appointy calendar.
Should you want to add reviews on Google Maps (local business listing), you can achieve that by customizing your "Thank You" email from SETTINGS>>CUSTOMIZE section of Appointy admin. All you need to do is add a link to your review in the "Thank you" email, and you are good to go.
Note: Customization is a part of PRO and above memberships.