updates reamde (#100)

Author: martinmckenna

README.md

@@ -1,5 +1,9 @@
 ![Iterable-Logo](https://user-images.githubusercontent.com/7387001/129065810-44b39e27-e319-408c-b87c-4d6b37e1f3b2.png)
 
+# BETA FEATURE
+
+:rotating_light: Web in-app messages (along with the Iterable Web SDK) are in Beta. If you'd like to try them out, talk to your customer success manager. We cannot guarantee this SDK will function as expected if you are not in the Beta program. :rotating_light:
+
 # Iterable's Web SDK
 
 [Iterable](https://www.iterable.com) is a growth marketing platform that helps you to create better experiences for—and deeper relationships with—your customers. Use it to send customized email, SMS, push notification, in-app message, web push notification campaigns to your customers.