Document NVTX ranges in CUB device algorithms

cub/docs/developer_overview.rst

@@ -744,3 +744,16 @@ contains hidden visibility attribute.
 
 To satisfy (3), CUB symbols are placed inside an inline namespace containing the set of
 GPU architectures for which the TU is being compiled.
+
+
+NVTX
+************************************
+
+The `NVIDIA Tools Extension SDK (NVTX) <https://nvidia.github.io/NVTX/>`_ is a cross-platform API
+for annotating source code to provide contextual information to developer tools.
+All device-scope algorithms in CUB are annotated with NVTX ranges,
+allowing their start and stop to be visualized in profilers
+like `NVIDIA Nsight Systems <https://developer.nvidia.com/nsight-systems>`_.
+Only the public APIs available in the ``<cub/device/device_xxx.cuh>`` headers are annotated,
+excluding direct calls to the dispatch layer.
+NVTX annotations can be disabled by defining ``NVTX_DISABLE`` during compilation.