Add new page to index

Signed-off-by: Julian Oppermann <[email protected]>

Author: jopperm

sycl/doc/index.rst

@@ -56,6 +56,7 @@ Design Documents for the oneAPI DPC++ Compiler
    design/PrivateAlloca
    design/SYCLBINDesign
    design/PropertySets
+   design/SYCL-RTC
    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>
    design/Fuzzing