Add alternative way to investigate MUST html files

doc.zih.tu-dresden.de/docs/software/mpi_usage_error_detection.md

@@ -214,8 +214,10 @@ from the [MUST documentation v1.7.2](https://hpc.rwth-aachen.de/must/files/Docum
     marie@local$ scp -r taurus.hrsk.tu-dresden.de:/scratch/ws/0/marie-must/{MUST_Output-files,MUST_Output.html}
     ```
 
-    and open the file `MUST_Output.html` using a webbrowser. MUST detects all three MPI usage errors
-    within this example:
+    and open the file `MUST_Output.html` using a webbrowser. Alternativly, you can open the html file with a
+    `firefox` instance on the HPC sytems. This requires to [forward the X11 support via SSH](../access/ssh_login.md#x11-forwarding).
+    
+    MUST detects all three MPI usage errors within this example:
 
     * A type mismatch
     * A send-send deadlock