docs: Update explanatory comment about impactedThreads

Author: KevinBoulongne

app/src/main/java/com/infomaniak/mail/data/cache/mailboxContent/RefreshStrategies.kt

@@ -30,7 +30,10 @@ interface RefreshStrategy {
     fun queryFolderThreads(folderId: String, realm: TypedRealm): List<Thread>
 
     /**
-     * The returned Threads should be managed by Realm
+     * About the `impactedThreadsManaged`:
+     *  This set will be updated throughout the whole process of handling added Messages.
+     *  It represents all the Threads that have been concerned by adding new Messages in the current Folder.
+     *  It should be the full set given everywhere, because sometimes we are adding Threads to it, and sometimes we are removing.
      */
     fun handleAddedMessages(
         scope: CoroutineScope,