List restrictions for Nvidia and AMD devices

Author: gmlueck

sycl/doc/extensions/experimental/sycl_ext_oneapi_device_architecture.asciidoc

@@ -585,6 +585,11 @@ feature, the application must be compiled in ahead-of-time (AOT) mode using
 description of the `-fsycl-targets` option.  These are the target names of the
 form "intel_gpu_*", "nvidia_gpu_*", or "amd_gpu_*".
 
+The two APIs `device::ext_oneapi_architecture_is` and the
+`ext::oneapi::experimental::info::device::architecture` device descriptor are
+currently supported only for Intel devices (both GPU and CPU).  There is no
+support yet for Nvidia or AMD devices.
+
 
 == Future direction