orte-rmaps-base: slightly amend help message

Follow on to 430c659908: clarify the help message and fix one typo.

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>

orte/mca/rmaps/base/help-orte-rmaps-base.txt

@@ -37,12 +37,11 @@ environment in which Open MPI processes are run:
 
   1. Hostfile, via "slots=N" clauses (N defaults to number of
      processor cores if not provided)
-  2. The --host:N command line parameter (N defaults to 1 if not
+  2. The --host command line parameter, via a ":N" suffix on the
-     provided)
+     hostname (N defaults to 1 if not provided)
   3. Resource manager (e.g., SLURM, PBS/Torque, LSF, etc.)
-  4. If neither a hostfile, the --hosts command line parameter, nor an
+  4. If none of a hostfile, the --host command line parameter, or an
-     RM is present, Open MPI defaults to the number of processor
+     RM is present, Open MPI defaults to the number of processor cores
-     cores
 
 In all the above cases, if you want Open MPI to default to the number
 of hardware threads instead of the number of processor cores, use the