[orx-compositor] Add demo description

orx-compositor/src/jvmDemo/kotlin/DemoAside01.kt

@@ -6,6 +6,19 @@ import org.openrndr.extra.fx.blur.HashBlurDynamic
 import org.openrndr.extra.fx.patterns.Checkers
 import kotlin.math.cos
 
+/**
+ * Demonstrates how to reuse a layer in the Compositor by using `aside { }`.
+ *
+ * The `aside` block can make use of `draw`, `mask` and `post`. In this demo
+ * only the latter is used to apply a full-window animated `Checkers` effect.
+ * The `aside` is not displayed by default.
+ *
+ * Next, a white, centered circle is drawn.
+ *
+ * Finally, a `HashBlurDynamic` post-processing effect is applied. The dynamic
+ * version of the HashBlur effect multiplies its `radius` argument by the red component
+ * of the provided texture (containing the animated checkers in this case).
+ */
 fun main() = application {
     configure {
         width = 720