Update README.md (#75)

Author: wolfy-j

README.md

@@ -2,8 +2,6 @@
 
 [![CI Status](https://github.com/temporalio/php-sdk/workflows/Unit/badge.svg)](https://github.com/temporalio/php-sdk/actions)
 
-**Attention, the package is under development.**
-
 ## Introduction
 
 Temporal is a distributed, scalable, durable, and highly available orchestration