Improve the wording. Add a note about exceptions.

Author: akukanov

source/elements/oneDPL/source/parallel_api/execution_policies.rst

@@ -168,12 +168,13 @@ It is a global immutable (``const``) instance of type ``device_policy<>``.
 [*Note*: ``dpcpp_default`` can be copied but cannot be moved. -- *end note*]
 
 ``dpdefault``, ``dpgpu``, and `dpcpu`` are variable templates for creating ``device_policy`` objects,
-possibly with user-provided kernel names, to run algorithms on the default SYCL device, a GPU device,
-and a CPU device, respectively. A policy object instantiated from one of these templates is associated
-with a SYCL queue constructed with the device selector appropriate for the template used.
+possibly with explicit kernel names, to run algorithms on the default SYCL device, a GPU device,
+and a CPU device, respectively. An object instantiated from one of these templates is a global
+immutable ``device_policy`` object. It is associated with a SYCL queue constructed with
+the SYCL device selector that corresponds to the used variable template.
 [*Example*: ``dpgpu<>`` is associated with a queue created by ``sycl::gpu_selector_v``. -- *end example*]
 
-
+Creation or use of a `dpgpu` or a `dpcpu` policy object can throw ``sycl::exception`` if no appropriate device is found.
 
 make_device_policy Function
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^