Merge pull request #666 from Unity-Technologies/volume-fixes2

Fixed Volume.Add() not adding anything 💯

ScriptableRenderPipeline/Core/Volume/Volume.cs

 
             var component = ScriptableObject.CreateInstance<T>();
             component.SetAllOverridesTo(overrides);
+            components.Add(component);
             isDirty = true;
             return component;
         }