README: add RGB color conversion example

Author: stokito

README.md

@@ -57,6 +57,8 @@ conv.hsluv_s = 75;
 conv.hsluv_l = 65;
 conv.hsluvToHex();
 System.out.println(conv.hex); // Will print "#ec7d82"
+double[] rgb = new double[] {conv.rgb_r, conv.rgb_g, conv.rgb_b};
+Color color = new Color(rgb[0], rgb[1], rgb[2]);
 ```
 
 # Testing