NEWS: Update bullet about PMIx improvements.

Per the call/discussion today, we want to make it clear that the
improvements are only when you are actually using PMIx (via
mpirun-based launches and when using a RM that utilizes PMIX
[vs. PMI-2 or the like]).

Signed-off-by: Jeff Squyres <[email protected]>

Author: jsquyres

NEWS

@@ -59,8 +59,10 @@ included in the vX.Y.Z section and be denoted as:
 Major new features:
 
 - The main focus of the Open MPI v2.1.0 release was to update to PMIx
-  v1.2.1, improving launch time scalability, and greatly decreasing
-  the memory footprint when launching large numbers of MPI / OSHMEM
+  v1.2.1.  When using PMIx (e.g., via mpirun-based launches, or direct
+  launches with recent versions of popular resource managers), launch
+  time scalability is improved, and the run time memory footprint is
+  greatly decreased when launching large numbers of MPI / OpenSHMEM
   processes.
 - Update OpenSHMEM API conformance to v1.3.
 - The usnic BTL now supports MPI_THREAD_MULTIPLE.