DOC: Intel MPI GPU offload update (uxlfoundation#2145)

doc/sources/distributed-mode.rst

@@ -28,6 +28,14 @@ via ``impi-devel`` python package) and the ``mpi4py`` python package. If using |
 `installed from sources <https://github.com/intel/scikit-learn-intelex/blob/main/INSTALL.md#build-from-sources>`_,
 ensure that the spmd_backend is built.
 
+Note that |intelex| now supports GPU offloading to speed up MPI operations. This is supported automatically with 
+some MPI backends, but in order to use GPU offloading with Intel MPI, set the following environment variable (providing
+data on device without this may lead to a runtime error):
+
+::
+
+     export I_MPI_OFFLOAD=1
+
 Estimators can be imported from the ``sklearnex.spmd`` module. Data should be distributed across multiple nodes as 
 desired, and should be transfered to a dpctl or dpnp array before being passed to the estimator. View a full 
 example of this process in the |intelex| repository, where many examples of our SPMD-supported estimators are