Update help.md

docs/help.md

@@ -11,6 +11,15 @@ Issue | Workarounds
 :--- | :---
 glTF export failed. | ① Retry but when PBR plugin asks: "Propagate materials to whole model?", answer: "Yes". ② Be sure **all** texture images are in JPEG or PNG format. Else, convert them with a tool like [this](https://image.online-convert.com/convert-to-png) then reimport them in SketchUp.
 
+### How to add a light to model?
+
+1. If it's not already exists, create a new layer and name it **exactly** `PBR Lights`.
+2. Add any object. It will be your light. Group it then assign it to layer `PBR Lights`.<br/>
+To ease this process, I recommand [Shapes](https://extensions.sketchup.com/content/shapes). It creates already grouped shapes. 
+3. Reopen PBR Viewport and voilà!
+
+You can paint your light/object with a color. You can add many lights to model.
+
 ### How to uninstall PBR plugin?
 
 Open Extension Manager. Disable PBR plugin **before** uninstall it.