Documentation of the API change is added.

CHANGES.md

@@ -21,6 +21,7 @@ Translations 🗣:
 
 SDK API changes ⚠️:
  - Get crypto methods through Session.cryptoService()
+ - ProgressListener.onProgress() function will be invoked on the background thread instead of UI thread
 
 Build 🧱:
  -

matrix-sdk-android/src/main/java/im/vector/matrix/android/api/listeners/ProgressListener.kt

@@ -20,7 +20,7 @@ package im.vector.matrix.android.api.listeners
  * Interface to send a progress info
  */
 interface ProgressListener {
-    /**
+    /** Will be invoked on the background thread, not in UI thread.
      * @param progress from 0 to total by contract
      * @param total
      */