Fix broken links to MPI doc. (horovod#2913)

Signed-off-by: Ryan <[email protected]>

Author: rb-determined-ai

docs/running.rst

@@ -62,7 +62,7 @@ Usage of ``horovodrun`` requires one of the following:
 If you do not have MPI installed, you can run ``horovodrun`` using Gloo.  Gloo dependencies come with Horovod
 automatically, and only require CMake to be available on your system at the time you install Horovod.
 
-If you wish to use a different version of MPI, you may still be able to run Horovod using `mpirun <mpirun.rst>`
+If you wish to use a different version of MPI, you may still be able to run Horovod using `mpirun <mpi.rst>`
 directly.
 
 
@@ -96,12 +96,12 @@ Advanced: Run Horovod with Open MPI
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 In some advanced cases you might want fine-grained control over options passed to Open MPI.
 To learn how to run Horovod training directly using Open MPI,
-read `Run Horovod with Open MPI <mpirun.rst>`_.
+read `Run Horovod with Open MPI <mpi.rst>`_.
 
 Run Horovod with Intel(R) MPI
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 ``horovodrun`` automatically converts some parameters to the format supported by Intel(R) MPI ``mpirun``. The set of allowed options includes ``-np``, ``-H`` and
-ssh arguments (-p, -i). Intel(R) MPI ``mpirun`` does not support MCA parameters, but you can set some of the options via `environment variables <https://software.intel.com/content/www/us/en/develop/documentation/mpi-developer-reference-linux/environment-variable-reference.html>`__. 
+ssh arguments (-p, -i). Intel(R) MPI ``mpirun`` does not support MCA parameters, but you can set some of the options via `environment variables <https://software.intel.com/content/www/us/en/develop/documentation/mpi-developer-reference-linux/environment-variable-reference.html>`__.
 For additional information refer to `Intel(R) MPI official documentation <https://software.intel.com/content/www/us/en/develop/documentation/mpi-developer-reference-linux/top/command-reference/mpiexec-hydra/global-options.html>`__.
 
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