[orx-shapes] Add demo descriptions

orx-shapes/src/jvmDemo/kotlin/primitives/DemoArc01.kt

@@ -4,6 +4,16 @@ import org.openrndr.application
 import org.openrndr.color.ColorRGBa
 import org.openrndr.extra.shapes.primitives.Arc
 
+/**
+ * Shows how to create an `Arc` centered on the window. The start and end angles of the arc increase 36 degrees
+ * per second, resulting in an animated effect.
+ *
+ * The `contour` property of the arc is used for rendering.
+ *
+ * The start, mid and end points of the arc are queried using it's `position()` method
+ * to draw small circles at those locations.
+ *
+ */
 fun main() = application {
     configure {
         width = 720

orx-shapes/src/jvmDemo/kotlin/primitives/DemoNet01.kt

@@ -6,6 +6,16 @@ import org.openrndr.extra.shapes.primitives.Net
 import org.openrndr.shape.Circle
 import kotlin.math.sin
 
+/**
+ * Shows how to create and render a [Net]: a structure
+ * that connects two points with a circle in between,
+ * forming a string-like shape.
+ *
+ * The main circle moves following an invisible infinite sign,
+ * formed by a pair of sine functions. The moving circle is connected to
+ * two smaller static circles via a [Net], rendered as a white
+ * contour with a stroke weight 2 pixels wide.
+ */
 fun main() = application {
     program {
         extend {

orx-shapes/src/jvmDemo/kotlin/primitives/DemoPulley01.kt

@@ -6,6 +6,10 @@ import org.openrndr.extra.shapes.primitives.Pulley
 import org.openrndr.math.Vector2
 import org.openrndr.shape.Circle
 
+/**
+ * Demonstrates how to create and render a [Pulley]: a system defined by two circles
+ * connected by their outer tangents.
+ */
 fun main() = application {
     configure {
         width = 720
@@ -14,6 +18,7 @@ fun main() = application {
     program {
         extend {
             drawer.clear(ColorRGBa.BLACK)
+            drawer.strokeWeight = 8.0
             drawer.stroke = ColorRGBa.WHITE
             drawer.fill = ColorRGBa.PINK
             val pulley = Pulley(