Explain more specifically how to use flutter drive/what it does (#161450)

_Run integration tests for the project_ is not an accurate statement, as
there is nothing inherently about `flutter_driver` that is for
integration tests (for example, it could be just plain automation,
benchmarking, etc).

In addition, clarifies what the most common two arguments might be and
their defaults.

Co-authored-by: Andrew Kolos <andrewrkolos@gmail.com>

packages/flutter_tools/lib/src/commands/drive.dart

@@ -216,7 +216,11 @@ class DriveCommand extends RunCommandBase {
 
   @override
   final String description =
-      'Run integration tests for the project on an attached device or emulator.';
+      'Builds and installs the app, and runs a Dart program that connects to '
+      'the app, often to run externally facing integration tests, such as with '
+      'package:test and package:flutter_driver.\n'
+      '\n'
+      'Usage: flutter drive --target <lib/main.dart> --driver <test_driver/main_test.dart>.';
 
   @override
   String get category => FlutterCommandCategory.project;

packages/flutter_tools/test/commands.shard/hermetic/drive_test.dart

@@ -588,6 +588,32 @@ void main() {
       DeviceManager: () => fakeDeviceManager,
     },
   );
+
+  testUsingContext('flutter drive --help explains how to use the command', () async {
+    final DriveCommand command = DriveCommand(
+      fileSystem: fileSystem,
+      logger: logger,
+      platform: platform,
+      signals: signals,
+    );
+
+    // TODO(matanlurey): https://github.com/flutter/flutter/issues/158532.
+    final StringBuffer printOutput = StringBuffer();
+    final Zone capturePrintZone = Zone.current.fork(
+      specification: ZoneSpecification(
+        print: (_, _, _, String line) {
+          printOutput.writeln(line);
+        },
+      ),
+    );
+    await capturePrintZone.run(() async {
+      await createTestCommandRunner(command).run(<String>['drive', '--help']);
+    });
+    expect(
+      printOutput.toString(),
+      stringContainsInOrder(<String>['flutter drive', '--target', '--driver']),
+    );
+  });
 }
 
 class ThrowingScreenshotDevice extends ScreenshotDevice {