update runtime doc with note on SGI MPT preloading

darshan-runtime/doc/darshan-runtime.txt

@@ -219,7 +219,7 @@ should be compiled using the normal, unmodified MPI compiler.
 
 To use this mechanism, set the `LD_PRELOAD` environment variable to the full
 path to the Darshan shared library. The preferred method of inserting Darshan
-instrumentation in this case is to set the LD_PRELOAD variable specifically
+instrumentation in this case is to set the `LD_PRELOAD` variable specifically
 for the application of interest. Typically this is possible using
 command line arguments offered by the `mpirun` or `mpiexec` scripts or by
 the job scheduler:
@@ -249,6 +249,11 @@ unrelated binaries:
 export LD_PRELOAD=/home/carns/darshan-install/lib/libdarshan.so
 ----
 
+[NOTE]
+For SGI systems running the MPT environment, it may be necessary to set the `MPI_SHEPHERD`
+environment variable equal to `true` to avoid deadlock when preloading the Darshan shared
+library.
+
 === Instrumenting dynamically-linked Fortran applications
 
 Please follow the general steps outlined in the previous section.  For