HDRenderPipeline: Add some comment for reflection cubemap

ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/Lit.hlsl

         F = Sq(-F * bsdfData.coatCoverage + 1.0);
     }
 
+    // When we are rough, we tend to see outward shifting of the reflection when at the boundary of the projection volume
+    // Also it appear like more sharp. To avoid these artifact and at the same time get better match to reference we lerp to original unmodified reflection.
+    // Formula is empirical.
+
     float4 preLD = SampleEnv(lightLoopContext, lightData.envIndex, R, preLightData.iblMipLevel);
     envLighting += F * preLD.rgb;