Added information about HDRP not upgrading particle shaders (#1601)

* Added information about HDRP not upgrading particle shaders

* Update Upgrading-To-HDRP.md

* Update Upgrading-To-HDRP.md

com.unity.render-pipelines.high-definition/Documentation~/Upgrading-To-HDRP.md

@@ -59,7 +59,11 @@ You can find these options in either:
 
 * The Render Pipeline Wizard window, inside the **Project Migration Quick-links** section.
 
-This process can not automatically upgrade custom Materials or Shaders to HDRP. You must [convert custom Materials and Shaders manually](#ManualConversion).
+This process cannot automatically upgrade custom Materials or Shaders to HDRP. You must [convert custom Materials and Shaders manually](#ManualConversion). This process also cannot upgrade particle shaders. Even though HDRP does not support particle shaders, it does provide some Shader Graphs that are compatible with the [Built-in Particle System](https://docs.unity3d.com/Manual/Built-inParticleSystem.html). These Shader Graphs work in a similar way to the built-in particle shaders. To use these Shader Graphs, import the **Particle System Shader Samples** sample:
+
+1. Open the Package Manager window (menu: **Window > Package Manager**).
+2. Find and click the **High Definition RP** entry.
+3. In the package information for **High Definition RP**, go to the **Samples** section and click the **Import into Project** button next to **Particle System Shader Samples**.
 
 <a name="ManualConversion"></a>