Update CHANGELOG from m112 release (#3547)

* Update CHANGELOG from m112 release

* include full link to docsite

* Fix typo

Author: rachaprince

firebase-appdistribution/CHANGELOG.md

@@ -1,2 +1,17 @@
 # Unreleased
-- Initial public beta release
+
+# Released
+
+## v20.0.6 (M112)
+
+#### Android library
+* {{feature}} The Firebase App Distribution Android SDK is now available in beta. You
+  can use this SDK to notify testers in-app when a new test build is available.
+  To learn more, visit the
+  [reference documentation](https://firebase.google.com/docs/reference/android/com/google/firebase/appdistribution/package-summary).
+
+#### Kotlin extensions
+The Android library with Kotlin extensions is now available in
+beta. The Kotlin extensions library transitively includes the base
+`firebase-app-distribution` library. To learn more, visit the
+[KTX reference documentation](https://firebase.google.com/docs/reference/kotlin/com/google/firebase/appdistribution/ktx/package-summary).