[SYCL][NFC] Add a TODO comment promised during review of #4101

Signed-off-by: Vyacheslav N Klochkov <[email protected]>

Author: v-klochkov

sycl/source/detail/reduction.cpp

@@ -55,9 +55,10 @@ __SYCL_EXPORT uint32_t reduGetMaxNumConcurrentWorkGroups(
     std::shared_ptr<sycl::detail::queue_impl> Queue) {
   device Dev = Queue->get_device();
   uint32_t NumThreads = Dev.get_info<info::device::max_compute_units>();
-  // The heuristics require additional tuning for various devices and vendors.
-  // For now assuming that each of execution units have about 8 working threads
-  // gives good results on some known/supported GPU devices.
+  // TODO: The heuristics here require additional tuning for various devices
+  // and vendors. For now this code assumes that execution units have about
+  // 8 working threads, which gives good results on some known/supported
+  // GPU devices.
   if (Dev.is_gpu())
     NumThreads *= 8;
   return NumThreads;