Add hint in tutorials that unused cbuffers in shaders are not reflected (i.e. GetStaticVariableByName,.. does not work)

[simsevi]

One possible reason for this issue is that the HLSL compiler may optimize away unused cbuffer declarations, causing the shader reflection to overlook these buffers. As a result, when calling GetStaticVariableBy..., it returns a nullptr, and invoking ->Set subsequently triggers an exception. This is probably common knowledge for some but it might be helpful :) I am not sure if the same is true for other variable types.

[TheMostDiligent]

Same is true for any shader resource - if you declare it but not use, the compiler will optimize it out as if it was not declared.