Merge pull request #8176 from Unity-Technologies/internal/2021.3/staging

[Port] [2021.3] DOCG-7382 Small updates to HDRP shadows documentation

Author: claire-nicholson

Packages/com.unity.render-pipelines.high-definition/Documentation~/Override-Contact-Shadows.md

@@ -19,6 +19,8 @@ The property to enable in your Frame Settings is: **Lighting > Contact Shadows**
 
 You can enable Contact Shadows on a per Light basis for Directional, Point, and Spot Lights. Tick the **Enable** checkbox under the **Contact Shadows** drop-down in the **Shadows** section of each Light to indicate that HDRP should calculate Contact Shadows for that Light.
 
+If you use both contact shadows and [realtime shadows](realtime-shadows.md), there might be a visible seam between the two types of shadow. To avoid this issue, set shadow maps to use a high resolution. For more information, refer to [Control shadow resolution and quality](Shadows-in-HDRP.md).
+
 **Note**: A Light casts Contact Shadows for every Mesh Renderer that uses a Material that writes to the depth buffer. This is regardless of whether you enable or disable the **Cast Shadows** property on the Mesh Renderer. This means that you can disable **Cast Shadows** on small GameObjects/props and still have them cast Contact Shadows. This is good if you do not want HDRP to render these GameObjects in shadow maps. If you do not want this behavior, use Shader Graph to author a Material that does not write to the depth buffer.
 
 [!include[](snippets/volume-override-api.md)]

Packages/com.unity.render-pipelines.high-definition/Documentation~/Ray-Traced-Shadows.md

@@ -69,7 +69,7 @@ Ray-traced shadows allow for transparent and transmissive GameObjects, lit by Di
 | **Sample Count**      | Controls the number of rays that HDRP uses per pixel, per frame. Higher values produce more accurate shadows. Increasing this value increases execution time linearly. |
 | **Color Shadow**      | Allows transparent and transmissive GameObjects to cast colored shadows. A Material can only cast colored shadows when its [**Refraction Model**](Surface-Type.md#transparency-inputs) is set to **Thin**, **Box** or **Sphere**. |
 | **Denoise**           | Enables the spatio-temporal filter that HDRP uses to remove noise from the ray-traced shadows; making them smoother. |
-| - **Denoiser Radius** | Controls the radius of the spatio-temporal filter.           |
+| - **Denoiser Radius** | Increases or decreases the blurriness between ray traced shadows, by controlling the radius of the spatio-temporal filter. |
 
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