Add doc comments

packages/url_launcher/url_launcher_web/CHANGELOG.md

@@ -1,6 +1,6 @@
 # 0.0.2
 
-- Switch to using `url_launcher_platform_interface`
+- Switch to using `url_launcher_platform_interface`.
 
 # 0.0.1
 

packages/url_launcher/url_launcher_web/lib/url_launcher_web.dart

@@ -5,7 +5,11 @@ import 'package:flutter_web_plugins/flutter_web_plugins.dart';
 import 'package:meta/meta.dart';
 import 'package:url_launcher_platform_interface/url_launcher_platform_interface.dart';
 
+/// The web implementation of [UrlLauncherPlatform].
+///
+/// This class implements the `package:url_launcher` functionality for the web.
 class UrlLauncherPlugin extends UrlLauncherPlatform {
+  /// Registers this class as the default instance of [UrlLauncherPlatform].
   static void registerWith(Registrar registrar) {
     UrlLauncherPlatform.instance = UrlLauncherPlugin();
   }