add some documentation for mpirun's new --loadbalance option closing #1277

This commit was SVN r18832.

orte/tools/orterun/orterun.1

@@ -171,6 +171,11 @@ Provide a hostfile to use.
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 .
 .TP
+.B -loadbalance\fR,\fP --loadbalance
+Uniform distribution of ranks across all nodes by Round Robin mapper.
+.
+.
+.TP
 .B -machinefile\fR,\fP --machinefile \fR<machinefile>\fP
 Synonym for \fI-hostfile\fP.
 .
@@ -461,6 +466,16 @@ on each slot on a given node before running the executable on other available
 nodes.
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 .
+.SS Loadbalance rank allocation
+.
+Uniform distribution of the ranks on all nodes when using Round Robin mapper while retaining byslot rank associations.
+
+ ex :               byslot    bynode   loadbalance
+        node0:      0,1,2,3   0,3,6    0,1,2   
+        node1:      4,5,6     1,4      3,4
+        node2:                2,5      5,6
+.
+.
 .
 .SS Specifying Hosts
 .