Add link to MPICH page from main communication libraries page (#242)

Author: msimberg

docs/software/communication/index.md

@@ -4,15 +4,16 @@
 CSCS provides common communication libraries optimized for the [Slingshot 11 network on Alps][ref-alps-hsn].
 
 For most scientific applications relying on MPI, [Cray MPICH][ref-communication-cray-mpich] is recommended.
-[OpenMPI][ref-communication-openmpi] may also be used, with limitations.
-Both Cray MPICH and OpenMPI make use of [libfabric][ref-communication-libfabric] to interact with the underlying network.
+[MPICH][ref-communication-mpich] and [OpenMPI][ref-communication-openmpi] may also be used, with limitations.
+Cray MPICH, MPICH, and OpenMPI make use of [libfabric][ref-communication-libfabric] to interact with the underlying network.
 
 Most machine learning applications rely on [NCCL][ref-communication-nccl] or [RCCL][ref-communication-rccl] for high-performance implementations of collectives.
 NCCL and RCCL have to be configured with a plugin using [libfabric][ref-communication-libfabric] to make full use of the Slingshot network.
 
 See the individual pages for each library for information on how to use and best configure the libraries.
 
 * [Cray MPICH][ref-communication-cray-mpich]
+* [MPICH][ref-communication-mpich]
 * [OpenMPI][ref-communication-openmpi]
 * [NCCL][ref-communication-nccl]
 * [RCCL][ref-communication-rccl]