docs: add missing examples for effects

docs/effects/halftone.mdx

@@ -25,6 +25,10 @@ return (
 )
 ```
 
+## Example
+
+[![Halftone demo](https://pmndrs.github.io/examples/halftone/thumbnail.webp)](https://pmndrs.github.io/examples/halftone)
+
 ## Props
 
 | Name          | Type          | Default              | Description                                        |

docs/effects/kuwahara.mdx

@@ -22,6 +22,10 @@ return (
 
 The filter takes about `radius * sectorCount * 3` texture samples per pixel, so large radii get expensive quickly. Lower `sectorCount` when raising `radius`.
 
+## Example
+
+[![Kuwahara demo](https://pmndrs.github.io/examples/kuwahara/thumbnail.webp)](https://pmndrs.github.io/examples/kuwahara)
+
 ## Props
 
 | Name          | Type          | Default              | Description                                                   |

docs/effects/lens-distortion.mdx

@@ -18,6 +18,10 @@ return (
 )
 ```
 
+## Example
+
+[![LensDistortion demo](https://pmndrs.github.io/examples/lens-distortion/thumbnail.webp)](https://pmndrs.github.io/examples/lens-distortion)
+
 ## Props
 
 | Name           | Type          | Default              | Description                             |

docs/effects/lensflare.mdx

@@ -25,6 +25,10 @@ Use bvh `<bvh><Scene></bvh>` to enhance the internal raycaster performance.
 
 The Ultimate Lens Flare leverages the raycaster to examine the material type of objects and determine if they are `MeshTransmissionMaterial` or `MeshPhysicalMaterial`. It checks for the transmission parameter to identify glass-like materials. Therefore, for an object to behave like glass, its material should have either `transmission = 1` or `transparent = true` and `opacity = NUMBER`. The effect automatically interprets the opacity `NUMBER` value to determine the brightness of the flare.
 
+## Example
+
+[![LensFlare demo](https://pmndrs.github.io/examples/lensflare/thumbnail.webp)](https://pmndrs.github.io/examples/lensflare)
+
 ## Credits
 
 - https://www.shadertoy.com/view/4sK3W3

docs/effects/linocut.mdx

@@ -22,6 +22,10 @@ return (
 )
 ```
 
+## Example
+
+[![Linocut demo](https://pmndrs.github.io/examples/linocut/thumbnail.webp)](https://pmndrs.github.io/examples/linocut)
+
 ## Props
 
 | Name          | Type          | Default              | Description                                            |

docs/effects/lut.mdx

@@ -18,6 +18,10 @@ return (
 )
 ```
 
+## Example
+
+[![LUT demo](https://pmndrs.github.io/examples/lut/thumbnail.webp)](https://pmndrs.github.io/examples/lut)
+
 ## Props
 
 | Name                     | Type          | Default           | Description                                    |

docs/effects/sharpness.mdx

@@ -18,6 +18,10 @@ return (
 )
 ```
 
+## Example
+
+[![Sharpness demo](https://pmndrs.github.io/examples/sharpness/thumbnail.webp)](https://pmndrs.github.io/examples/sharpness)
+
 ## Props
 
 | Name          | Type          | Default              | Description                                  |