Add design doc to TOC

Signed-off-by: Larsen, Steffen <[email protected]>

Author: steffenlarsen

sycl/doc/index.rst

@@ -47,6 +47,7 @@ Design Documents for the oneAPI DPC++ Compiler
    design/ESIMDDesignNotes
    design/DeviceIf
    design/NonRelocatableDeviceCode
+   design/DeviceAspectTraitDesign
    New OpenCL Extensions <https://github.com/intel/llvm/tree/sycl/sycl/doc/design/opencl-extensions>
    New SPIR-V Extensions <https://github.com/intel/llvm/tree/sycl/sycl/doc/design/spirv-extensions>