[orx-shader-phrases] Update README.md

Add an example, since there are no demos and it's not part of the guide.

orx-shader-phrases/README.md

@@ -4,7 +4,7 @@ A library that provides a `#pragma import` statement for shaders.
 
 ## Usage
 
-Work in progress.
+*Work in progress.*
 
 
 We can use the `preprocessShader()` function to resolve `#pragma import` statements.
@@ -19,3 +19,53 @@ Alternatively loading and preprocessing can be combined in a single function cal
     val preprocessedSource = preprocessShaderFromUrl(resourceUrl("/some-shader.frag"))
 ```
 
+## Example
+
+```kotlin
+import org.openrndr.application
+import org.openrndr.draw.shadeStyle
+import org.openrndr.extra.shaderphrases.ShaderPhrase
+import org.openrndr.extra.shaderphrases.ShaderPhraseBook
+import org.openrndr.extra.shaderphrases.preprocessShader
+
+// 1. Define GLSL functions to reuse in multiple files or programs.
+// Typically these will be larger blocks of code.
+// Note that the Kotlin variable name do not matter, but the used GLSL function name must match the #pragma import.
+class ColorShaderPhrases : ShaderPhraseBook("colors") {
+    val fRed = ShaderPhrase(
+        "vec3 red() { return vec3(1.0, 0.0, 0.0); }"
+    )
+
+    val fGreen = ShaderPhrase(
+        "vec3 green() { return vec3(0.0, 1.0, 0.0); }"
+    )
+
+    val fBlue = ShaderPhrase(
+        "vec3 blue() { return vec3(0.0, 0.0, 1.0); }"
+    )
+}
+
+fun main() = application {
+    program {
+        // 2. Make defined GLSL functions available
+        ColorShaderPhrases().register()
+
+        extend {
+            drawer.shadeStyle = shadeStyle {
+                // 3. Import the GLSL functions needed in this program
+                fragmentPreamble = preprocessShader("""
+                    #pragma import colors.red
+                    #pragma import colors.blue
+                """.trimIndent())
+
+                // 4. Make use of the available GLSL functions
+                fragmentTransform = """
+                    x_stroke.rgb = red();
+                    x_fill.rgb = blue();
+                """.trimIndent()
+            }
+            drawer.circle(drawer.bounds.center, 100.0)
+        }
+    }
+}
+```