docs: update changelog

Author: HamdaanAliQuatil

CHANGELOG.md

@@ -1,5 +1,8 @@
 # 0.6.0
 * Replaced the `KeyPair` class with `typedef KeyPair<T, S> = ({T privateKey, S publicKey})` and refactored key generation methods to return a named record.
+* Moved the following operations off the main thread with `Isolate`:
+  - `generateRsaKeyPair`
+  
 
 # 0.5.8
 * All classes previously annotated `@sealed` are now `final`!