Add deprecation notice to README

Added deprecation notice regarding repository updates.

Author: 73rhodes

README.md

@@ -1,8 +1,12 @@
+# Deprecation notice
+
+Zendesk is no longer automatically updating this repository based on changes to the Sunshine Conversations OpenAPI specification. We encourage users to refer to the [Sunshine Conversations OpenAPI specification](https://github.com/zendesk/sunshine-conversations-api-spec) and our [Developer Documentation](https://developer.zendesk.com/documentation/conversations/) for details on working with the Sunshine Conversations API.
+
 # sunshine-conversations-ruby
 
 SunshineConversationsClient - the Ruby gem for the Sunshine Conversations API
 
-This SDK is automatically generated by the [OpenAPI Generator Codegen](https://github.com/OpenAPITools/openapi-generator) project using the [Sunshine Conversations API spec](https://github.com/zendesk/sunshine-conversations-api-spec).
+This SDK has been automatically generated by the [OpenAPI Generator Codegen](https://github.com/OpenAPITools/openapi-generator) project using the [Sunshine Conversations API spec](https://github.com/zendesk/sunshine-conversations-api-spec).
 
 - API version: 17.0.0
 - Package version: 17.0.0