update changelog (#530)

Author: mensfeld

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## 0.20.0 (Unreleased)
 - [Enhancement] Bump librdkafka to 2.6.1
 - [Enhancement] Expose `rd_kafka_global_init` to mitigate macos forking issues.
+- [Enhancement] Avoid clobbering LDFLAGS and CPPFLAGS if in a nix prepared environment (secobarbital).
 - [Patch] Retire no longer needed cooperative-sticky patch.
 
 ## 0.19.0 (2024-10-01)