DOCG-8438 Add BIRP deprecation notice

Author: fatimah-mf-unity

com.unity.postprocessing/Documentation~/requirements.md

@@ -12,10 +12,13 @@ The **Post processing** package is compatible with the following versions of the
 
 This package is compatible with the following render pipeline versions:
 
-* Built-in render pipeline.
+* Built-In Render Pipeline.
 * Universal Render Pipeline (URP) 7.x, with Unity 2018 LTS, and 2019 LTS. Certain effects are not compatible with URP.
 * Scriptable Render Pipeline (SRP).
 
+> [!IMPORTANT]
+> In Unity 6.5 and newer, the Built-In Render Pipeline is deprecated and will be made obsolete in a future release. For more information, refer to [Migrating from the Built-In Render Pipeline to URP](https://docs.unity3d.com/6000.5/Documentation/Manual/urp/upgrading-from-birp.html) and [Render pipeline feature comparison](https://docs.unity3d.com/6000.5/Documentation/Manual/urp/upgrading-from-birp.html).
+
 ## Unity Player system requirements
 
 This package does not add any platform-specific requirements to Unity. For more information on Unity system requirements, see [System requirements for Unity](https://docs.unity3d.com/Manual/system-requirements.html).