Add a change log

Author: michaelklishin

CHANGELOG.md

@@ -0,0 +1,12 @@
+# RabbitMQ Objective-C and Swift Client Changelog
+
+## [0.12.0] - 2022-04-24
+
+ ### Fixed
+
+  * Eliminated a memory leak in environments where connections were closed and opened
+    dynamically during application operations.
+
+    Contributed by @BarryDuggan and @michaelklishin.
+
+    GitHub issue: [#198](https://github.com/rabbitmq/rabbitmq-objc-client/pull/198)