doc: add Offline Resources Loading.

Author: andycall

website/docs/tutorials/guides-for-flutter-developer/loading-web-contents-from-disk.md

@@ -0,0 +1,39 @@
+---
+sidebar_position: 5
+title: Offline Resources Loading
+---
+
+WebF supports the `https://`, `http://`, `file://`, and `assets://` protocols for fetching external resources.
+
+## `http://` and `https://` Protocols
+
+Like web browsers, the standard method to fetch remote resources is through the HTTP protocol.
+
+```dart
+controller = WebFController(
+  context,
+);
+controller.preload(WebFBundle.fromUrl('https://xxx.com/demo.html'));
+```
+
+## `file://` Protocol
+
+This protocol is used to access any disk location with readable permissions, available on both desktop and mobile platforms.
+
+```dart
+controller = WebFController(
+  context,
+);
+controller.preload(WebFBundle.fromUrl('file:///data/demo/demo.html'));
+```
+
+## `assets://` Protocol
+
+This protocol is used for resources bundled with Flutter assets.
+
+```dart
+controller = WebFController(
+  context,
+);
+controller.preload(WebFBundle.fromUrl('assets:///assets/bundle.html'));
+```