chore(readme): update example

Author: loonghao

README.md

@@ -67,7 +67,9 @@ app = ps.Application()
 doc = app.documents.add()
 new_doc = doc.artLayers.add()
 text_color = ps.SolidColor()
+text_color.rgb.red = 0
 text_color.rgb.green = 255
+text_color.rgb.blue = 0
 new_text_layer = new_doc
 new_text_layer.kind = ps.LayerKind.TextLayer
 new_text_layer.textItem.contents = 'Hello, World!'