HZN-801: Added documentation for the Edge Status Provider

opennms-doc/guide-development/src/asciidoc/text/topology/graphml.adoc

@@ -128,7 +128,26 @@ This can be achieved by setting the GraphML attribute `nodeID` on the GraphML No
 
 ==== Edge Status Provider
 
-TODO
+It is also possible to compute a status for each edge in a given graph.
+Just place Groovy scripts (with file extension .groovy) in the directory `$OPENNMS_HOME/etc/graphml-edge-status`.
+All of the scripts will be evaluated and the most severe status will be used for the edge in the topology's visualization.
+
+The following simple Groovy script example will apply a different style and severity if the edge's associated source node is down.
+
+.Scriptable edge status
+[source, groovy]
+----
+import org.opennms.netmgt.model.OnmsSeverity;
+import org.opennms.features.topology.plugins.topo.graphml.GraphMLEdgeStatus;
+
+if ( sourceNode != null && sourceNode.isDown() ) {
+    return new GraphMLEdgeStatus(OnmsSeverity.WARNING, [ 'stroke-dasharray' : '5,5', 'stroke' : 'yellow', 'stroke-width' : '6' ]);
+} else {
+    return new GraphMLEdgeStatus(OnmsSeverity.NORMAL, []);
+}
+----
+
+If the script shouldn't contribute any status to an edge just return null.
 
 [[gd-topology-graphml-layers]]
 ==== Layers