Link to dartlang.org in pub's command-line help messages.

sdk/lib/_internal/pub/lib/src/command/serve.dart

Index: sdk/lib/_internal/pub/lib/src/command/serve.dart
diff --git a/sdk/lib/_internal/pub/lib/src/command/serve.dart b/sdk/lib/_internal/pub/lib/src/command/serve.dart
index 0c56f2aae87e405401b1d727cd165f710a430654..1699797b8577ab1b3919aa6b0b971986f02b51eb 100644
--- a/sdk/lib/_internal/pub/lib/src/command/serve.dart
+++ b/sdk/lib/_internal/pub/lib/src/command/serve.dart
@@ -24,6 +24,7 @@ class ServeCommand extends BarbackCommand {
       'By default, this serves "web/" and "test/", but an explicit list of \n'
       'directories to serve can be provided as well.';
   String get usage => "pub serve [directories...]";
+  String get docUrl => "http://dartlang.org/tools/pub/cmd/pub-serve.html";
 
   PubPackageProvider _provider;