Add plugin url_launcher for Help page.

pubspec.lock

@@ -75,6 +75,11 @@ packages:
     description: flutter
     source: sdk
     version: "0.0.0"
+  flutter_web_plugins:
+    dependency: transitive
+    description: flutter
+    source: sdk
+    version: "0.0.0"
   leak_tracker:
     dependency: transitive
     description:
@@ -328,6 +333,70 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.4.0"
+  url_launcher:
+    dependency: "direct main"
+    description:
+      name: url_launcher
+      sha256: "9d06212b1362abc2f0f0d78e6f09f726608c74e3b9462e8368bb03314aa8d603"
+      url: "https://pub.dev"
+    source: hosted
+    version: "6.3.1"
+  url_launcher_android:
+    dependency: transitive
+    description:
+      name: url_launcher_android
+      sha256: "1d0eae19bd7606ef60fe69ef3b312a437a16549476c42321d5dc1506c9ca3bf4"
+      url: "https://pub.dev"
+    source: hosted
+    version: "6.3.15"
+  url_launcher_ios:
+    dependency: transitive
+    description:
+      name: url_launcher_ios
+      sha256: "16a513b6c12bb419304e72ea0ae2ab4fed569920d1c7cb850263fe3acc824626"
+      url: "https://pub.dev"
+    source: hosted
+    version: "6.3.2"
+  url_launcher_linux:
+    dependency: transitive
+    description:
+      name: url_launcher_linux
+      sha256: "4e9ba368772369e3e08f231d2301b4ef72b9ff87c31192ef471b380ef29a4935"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.2.1"
+  url_launcher_macos:
+    dependency: transitive
+    description:
+      name: url_launcher_macos
+      sha256: "17ba2000b847f334f16626a574c702b196723af2a289e7a93ffcb79acff855c2"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.2.2"
+  url_launcher_platform_interface:
+    dependency: transitive
+    description:
+      name: url_launcher_platform_interface
+      sha256: "552f8a1e663569be95a8190206a38187b531910283c3e982193e4f2733f01029"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.3.2"
+  url_launcher_web:
+    dependency: transitive
+    description:
+      name: url_launcher_web
+      sha256: "3ba963161bd0fe395917ba881d320b9c4f6dd3c4a233da62ab18a5025c85f1e9"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.4.0"
+  url_launcher_windows:
+    dependency: transitive
+    description:
+      name: url_launcher_windows
+      sha256: "3284b6d2ac454cf34f114e1d3319866fdd1e19cdc329999057e44ffe936cfa77"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.1.4"
   vector_math:
     dependency: transitive
     description: