add installation instructions to pkg packages

pkg/http/lib/http.dart

Index: pkg/http/lib/http.dart
diff --git a/pkg/http/lib/http.dart b/pkg/http/lib/http.dart
index 07457cdc347df6187cab8e27f0efb53d628b1855..c45285abaf7d55942cc024e69bfa613e12686e26 100644
--- a/pkg/http/lib/http.dart
+++ b/pkg/http/lib/http.dart
@@ -4,6 +4,16 @@
 
 /// A composable, [Future]-based library for making HTTP requests.
 ///
+/// ## Installing ##
+///
+/// Use [pub][] to install this package. Add the following to your
+/// `pubspec.yaml` file.
+///
+///     dependencies:
+///       http: any
+///
+/// And then run `pub install`.
+///
 /// The easiest way to use this library is via the top-level functions. They
 /// allow you to make individual HTTP requests with minimal hassle:
 ///
@@ -50,6 +60,8 @@
 ///         return _inner.send(request);
 ///       }
 ///     }
+///
+/// [pub]: http://pub.dartlang.org
 library http;
 
 import 'dart:async';