[Port] [2021.3] DOCG-6464 Add steps to 2D sprite lit shader graph URP docs

**This is a backport of https://github.cds.internal.unity3d.com/unity/unity/pull/59127**

Add steps to the 2D sprite lit shader graph URP docs, to clarify connecting up transparency/alpha, and setting the normal map input. Response to user feedback.

Jira tickets:

- https://jira.unity3d.com/browse/DOCG-6464
- https://jira.unity3d.com/browse/DOCG-6465

Author: markg-unity

Packages/com.unity.render-pipelines.universal/Documentation~/ShaderGraph.md

@@ -30,7 +30,12 @@
 7. Drag each of the **Texture 2D** properties onto the editor window. Attach each of the properties to the **Input Slots** of the Sample Texture 2D Nodes as shown below. Note that the 'NormalMap' property must be attached to the **Normal Type** Node only.
    ![](Images/2D/2d-urp12-3-attach-properties.png)
    <br/>
-8. Select **Save Asset** to save the Shader.
+
+8. Select the **NormalMap** property, then in the **Graph Inspector** set **Mode** to **Normal Map**.
+
+9. If your sprite texture has transparency, attach the alpha (**A**) output of the **Base Color** texture to the **Alpha** input of the **Fragment** context.
+
+10. Select **Save Asset** to save the Shader.
    ![](Images/2D/2d-urp12-3-save-shader.png)
 
 You can now apply the newly built Shader to materials.