Update README.md (#53)

* Update README.md

* Update README.md

Author: nick-zh

README.md

@@ -16,7 +16,8 @@ can help out to understand the internals of this library.
 
 ## Requirements
 - php: ^7.3
-- ext-rdkafka: ^4.0.0
+- ext-rdkafka: >=4.0.0
+- librdkafka: >=0.11.6 (if you use `<librdkafka:1.x` please define your own error callback)
 
 ## Installation
 ```