add example "texture_outline"

Which demonstrates shader support

build.zig

@@ -50,6 +50,11 @@ pub fn build(b: *Builder) void {
             .path = "examples/core/2d_camera.zig",
             .desc = "Shows the functionality of a 2D camera",
         },
+        .{
+            .name = "texture_outline",
+            .path = "examples/shaders/texture_outline.zig",
+            .desc = "Uses a shader to create an outline around a sprite",
+        },
         // .{
         //     .name = "models_loading",
         //     .path = "examples/models/models_loading.zig",