Update integration_tests README (#24142)

dev/integration_tests/README.md

diff --git a/dev/integration_tests/README.md b/dev/integration_tests/README.md
index b385c93..ecd7e9e 100644
--- a/dev/integration_tests/README.md
+++ b/dev/integration_tests/README.md
@@ -1,4 +1,6 @@
-Automated Flutter integration test suites. Each suite consists of a complete
-Flutter app and a `flutter_driver` specification that drives tests from the UI.
+Automated Flutter integration test suites. Each suite consists of either a
+complete Flutter app and a `flutter_driver` specification that drives tests
+from the UI, or a native app that is meant to integrate with Flutter for
+testing.
 
 Intended for use with devicelab.