build: Add changelog to iOS fastfile

ios/fastlane/Fastfile

@@ -27,7 +27,11 @@ platform :ios do
     version_name = config.match(re).captures[0]
     increment_version_number(version_number: version_name)
     build_app(workspace: "Runner.xcworkspace", scheme: "Runner")
-    upload_to_testflight(distribute_external: true, groups: "FluffyChat Betatest")
+    upload_to_testflight(
+      distribute_external: true,
+      groups: "FluffyChat Betatest",
+      changelog: "This is a release candidate for FluffyChat. Please test if the app is overall in a good condition before we push this to production.",
+    )
   end
 end