docs: Add disclaimer to readme. (#52)

* Add disclaimer to readme.

* Update README.md

README.md

@@ -2,6 +2,11 @@
 
 Java idiomatic client for Google Pub/Sub Lite.
 
+# Disclaimer
+
+This is the client library for an upcoming cloud product to be released shortly. It may not function
+due to restricted visibility for a short period of time. Please watch the Cloud Pub/Sub release notes for updates on availability. https://cloud.google.com/pubsub/docs/release-notes
+
 ## Quickstart
 
 If you are using Maven, add this to your pom.xml file