add clarifications on FI_OFI_RXM_USE_SRX and FI_VERBS_PREFER_XRC for MPI apps with >=64 ranks

maestro/core.c

@@ -610,6 +610,7 @@ mstro_core_init(const char *workflow_name,
     ERR("If your job terminates after this error please check\n"
         " ... that firewalling is not prohibiting libfabric communication\n"
         " ... that ulimit -n is high enough to keep a couple of FDs per network endpoints open (ulimit -n 1024 is a good start)\n"
+	" ... that FI_OFI_RXM_USE_SRX=1 and FI_VERBS_PREFER_XRC=0 with large MPI applications (>=64 ranks) when using verbs provider, especially with Cray MPICH\n"
 	" ... that your workflow-name/component-name/component-index triple is correct\n");
     goto BAILOUT;
   }