Add env var section to topology web page

Add description of SLURM_TOPOLOGY_ADDR and SLURM_TOPOLOGY_ADDR_PATTERN
environment variables to the topology web page.

doc/html/topology.shtml

@@ -142,6 +142,25 @@ The system administrator can limit the maximum time that any job can
 wait for this optimized configuration using the <i>SchedulerParameters</i>
 configuration parameter with the <i>max_switch_wait</i> option.</p>
 
-<p style="text-align:center;">Last modified 13 August 2013</p>
+<h2>Environment Variables</h2>
+
+<p>if the topology/tree plugin is used, two environment variables will be set
+to describe that jobs network topology. Note that these environment variables
+will contain different data for the tasks launched on each node. Use of these
+environment variables is at the discression of the user.</p>
+
+<p><b>SLURM_TOPOLOGY_ADDR</b>:
+The value will be set to the names network switches which may be involved in
+the job's communications from the system's top level switch down to the leaf
+switch and ending with node name. A period is used to separate each hardware
+component name.</p>
+
+<p><b>SLURM_TOPOLOGY_ADDR_PATTERN</b>:
+This is set only if the system has the topology/tree plugin configured.
+The value will be set component types listed in SLURM_TOPOLOGY_ADDR.
+Each component will be identified as either "switch" or "node".
+A period is used to separate each hardware component type.</p>
+
+<p style="text-align:center;">Last modified 13 January 2014</p>
 
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