Format the README a bit and shape up some of the text about MXM.

Still need a bit more, though.

This commit was SVN r24982.

README

@@ -140,7 +140,7 @@ Detailed Open MPI v1.5 Feature List:
       process)
     - Many other small improvements and bug fixes, too numerous to
       list here
-	- Mellanox MXM MTL layer implementation
+    - Mellanox MXM MTL layer implementation
 
 Known issues
 ------------
@@ -494,14 +494,14 @@ Network Support
     performance:
     - Myrinet MX (including Open-MX, but not GM)
     - InfiniPath PSM
-	- Mellanox MXM
+    - Mellanox MXM
     - Portals
 
   Open MPI will, by default, choose to use "cm" when the InfiniPath
-  PSM or Mellanox MXM MTL can be used.  Otherwise, "ob1" will be used and the
+  PSM or the Mellanox MXM MTL can be used.  Otherwise, "ob1" will be
-  corresponding BTLs will be selected.  "csum" will never be selected
+  used and the corresponding BTLs will be selected.  "csum" will never
-  by default.  Users can force the use of ob1 or cm if desired by
+  be selected by default.  Users can force the use of ob1 or cm if
-  setting the "pml" MCA parameter at run-time:
+  desired by setting the "pml" MCA parameter at run-time:
 
     shell$ mpirun --mca pml ob1 ...
     or
@@ -509,8 +509,11 @@ Network Support
     or
     shell$ mpirun --mca pml cm ...
 
-- MXM MTL is an transport layer utilizing various Mellanox proprietary
+- The MXM MTL is a transport layer utilizing various Mellanox
-  technologies and providing better scalability and performance for large scale jobs
+  proprietary InfiniBand-based technologies that provides better
+  scalability and performance for large-scale jobs.  
+
+  MXM will only work with ConnectX (or newer) HCAs.
 
 - Myrinet MX (and Open-MX) support is shared between the 2 internal
   devices, the MTL and the BTL.  The design of the BTL interface in
@@ -708,12 +711,12 @@ for a full list); a summary of the more commonly used ones follows:
   most cases.  This option is only needed for special configurations.
 
 --with-mxm=<directory>
-  Specify the directory where the Mellanox MXM library and
+  Specify the directory where the Mellanox MXM library and header
-  header files are located.  This option is generally only necessary
+  files are located.  This option is generally only necessary if the
-  if the MXM headers and libraries are not in default
+  MXM headers and libraries are not in default compiler/linker search
-  compiler/linker search paths.
+  paths.
 
-  MXM is the support library for Mellanox network adapters.
+  MXM is the support library for Mellanox ConnectX adapters.
 
 --with-mxm-libdir=<directory>
   Look in directory for the MXM libraries.  By default, Open MPI will