Better devices text (#3519)

* improve text for devices

* nit

* tweak text

packages/flutter_test/lib/src/widget_tester.dart

@@ -318,7 +318,7 @@ class CommonFinders {
   ///     expect(tester, hasWidget(find.byKey(backKey)));
   Finder byKey(Key key) => new _KeyFinder(key);
 
-  /// Finds widgets by searching for widgehts with a particular type.
+  /// Finds widgets by searching for widgets with a particular type.
   ///
   /// The `type` argument must be a subclass of [Widget].
   ///

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

@@ -33,7 +33,10 @@ class DevicesCommand extends FlutterCommand {
     List<Device> devices = await deviceManager.getAllConnectedDevices();
 
     if (devices.isEmpty) {
-      printStatus('No connected devices.');
+      printStatus(
+        'No devices detected.\n\n'
+        'If you expected your device to be detected, please run "flutter doctor" to diagnose\n'
+        'potential issues, or visit https://flutter.io/setup/ for troubleshooting tips.');
     } else {
       printStatus('${devices.length} connected ${pluralize('device', devices.length)}:\n');
       Device.printDevices(devices);