Update README.md

sky/packages/sky/README.md

@@ -75,12 +75,14 @@ expects to be run from the root directory of your application's package (i.e.,
 the same directory that contains the `pubspec.yaml` file). To run your app,
 follow these instructions:
 
- - The first time: `./packages/sky/sky_tool start --install && adb logcat -s sky chromium`
+ - The first time: `./packages/sky/sky_tool start --install --checked && adb logcat -s sky chromium`
 
- - Subsequent times: `./packages/sky/sky_tool start && adb logcat -s sky chromium`
+ - Subsequent times: `./packages/sky/sky_tool start --checked && adb logcat -s sky chromium`
 
 The `sky_tool start` command starts the dev server and uploads your app to the device.
 The `--install` flag installs `SkyShell.apk` if it is not already installed on the device.
+The `--checked` flag triggers checked mode, in which types are checked, asserts are run, and
+various [debugging features](lib/base/debug.dart) are enabled.
 The `adb logcat` command logs errors and Dart `print()` output from the app. The `-s sky chromium`
 argument limits the output to just output from Sky Dart code and the Sky Engine C++ code (which
 for historical reasons currently uses the tag `chromium`.)