Add text border docs (#36485)

packages/flutter/lib/src/painting/text_style.dart

@@ -166,6 +166,42 @@ const String _kColorBackgroundWarning = 'Cannot provide both a backgroundColor a
 /// ```
 /// {@end-tool}
 ///
+/// ### Borders and stroke
+///
+/// {@tool sample}
+/// To create bordered text, a [Paint] with [Paint.style] set to [PaintingStyle.stroke]
+/// should be provided as a [foreground] paint. The following example uses a [Stack]
+/// to produce a stroke and fill effect.
+///
+/// ![Text border](https://flutter.github.io/assets-for-api-docs/assets/widgets/text_border.png)
+///
+/// ```dart
+/// Stack(
+///   children: <Widget>[
+///     // Stroked text as border.
+///     Text(
+///       'Greetings, planet!',
+///       style: TextStyle(
+///         fontSize: 40,
+///         foreground: Paint()
+///           ..style = PaintingStyle.stroke
+///           ..strokeWidth = 6
+///           ..color = Colors.blue[700],
+///       ),
+///     ),
+///     // Solid text as fill.
+///     Text(
+///       'Greetings, planet!',
+///       style: TextStyle(
+///         fontSize: 40,
+///         color: Colors.grey[300],
+///       ),
+///     ),
+///   ],
+/// )
+/// ```
+/// {@end-tool}
+///
 /// ### Custom Fonts
 ///
 /// Custom fonts can be declared in the `pubspec.yaml` file as shown below: