[web] fix web_e2e_tests README (#92277)

dev/integration_tests/web_e2e_tests/README.md

 # Flutter Web integration tests
 
 To run the tests in this package [download][1] the chromedriver matching the
-version of Chrome. To find out the version of your Chrome installation visit chrome://version.
+version of Chrome. To find out the version of your Chrome installation visit
+chrome://version.
+
 Start `chromedriver` using the following command:
 
 ```
 chromedriver --port=4444
 ```
 
+An integration test is run using the `flutter drive` command. Some tests are
+written for a specific [web renderer][2] and/or specific [build mode][4].
+Before running a test, check the `_runWebLongRunningTests` function defined in
+[dev/bots/test.dart][3], and determine the right web renderer and the build
+mode you'd like to run the test in.
+
 Here's an example of running an integration test:
 
 ```
-flutter drive --target=test_driver/text_editing_integration.dart -d web-server --browser-name=chrome
+flutter drive --target=test_driver/text_editing_integration.dart \
+  -d web-server \
+  --browser-name=chrome \
+  --profile \
+  --web-renderer=html
 ```
 
+This example runs the test in profile mode (`--profile`) using the HTML
+renderer (`--web-renderer=html`).
+
 More resources:
 
 * chromedriver: https://chromedriver.chromium.org/getting-started
@@ -21,3 +36,6 @@ More resources:
 * `package:integration_test`: https://pub.dev/packages/integration_test
 
 [1]: https://chromedriver.chromium.org/downloads
+[2]: https://flutter.dev/docs/development/tools/web-renderers
+[3]: https://github.com/flutter/flutter/blob/master/dev/bots/test.dart
+[4]: https://flutter.dev/docs/testing/build-modes