Add an example reference map.

This can be as simple as a previous output of `birdc show ospf state`.

reference.ospf

@@ -0,0 +1,134 @@
+BIRD 2.0.9 ready.
+
+area 0.0.0.0
+
+	router 172.23.100.1
+		distance 30
+		network [172.23.100.4-3] metric 10
+		network [172.23.100.10-2] metric 10
+
+	router 172.23.100.2
+		distance 30
+		network [172.23.100.6-3] metric 10
+		network [172.23.100.10-2] metric 10
+
+	router 172.23.100.3
+		distance 40
+		network [172.23.100.8-3] metric 10
+		network [172.23.100.4-3] metric 10
+
+	router 172.23.100.4
+		distance 40
+		network [172.23.100.7-3] metric 10
+		network [172.23.100.4-3] metric 10
+
+	router 172.23.100.5
+		distance 40
+		network [172.23.100.8-3] metric 10
+		network [172.23.100.6-3] metric 10
+
+	router 172.23.100.6
+		distance 40
+		network [172.23.100.7-3] metric 10
+		network [172.23.100.6-3] metric 10
+
+	router 172.23.100.7
+		distance 50
+		network [172.23.100.9-2] metric 10
+		network [172.23.100.7-3] metric 10
+
+	router 172.23.100.8
+		distance 50
+		network [172.23.100.9-2] metric 10
+		network [172.23.100.8-3] metric 10
+
+	router 172.23.100.9
+		distance 60
+		network [172.23.100.9-2] metric 10
+
+	router 172.23.100.10
+		distance 20
+		network [172.23.100.10-2] metric 10
+		network [192.168.15.1-10] metric 10
+
+	router 192.168.15.1
+		distance 0
+		network [192.168.15.7-24] metric 10
+		network [192.168.15.1-10] metric 20
+		stubnet 192.168.101.0/24 metric 10
+		stubnet 192.168.201.0/24 metric 10
+
+	router 192.168.15.7
+		distance 10
+		network [192.168.15.7-24] metric 10
+		stubnet 192.168.15.0/24 metric 10
+		stubnet 192.168.0.0/24 metric 20
+		stubnet 192.168.42.0/24 metric 20
+		external 0.0.0.0/0 metric 50
+
+	router 192.168.15.10
+		distance 10
+		network [192.168.15.7-24] metric 10
+		external 0.0.0.0/0 metric 300
+
+	router 192.168.15.11
+		distance 10
+		network [192.168.15.7-24] metric 10
+		external 0.0.0.0/0 metric 300
+
+	network [172.23.100.4-3]
+		distance 40
+		router 172.23.100.4
+		router 172.23.100.1
+		router 172.23.100.3
+		address 172.23.4.0/24
+
+	network [172.23.100.6-3]
+		distance 40
+		router 172.23.100.6
+		router 172.23.100.5
+		router 172.23.100.2
+		address 172.23.5.0/24
+
+	network [172.23.100.7-3]
+		distance 50
+		router 172.23.100.7
+		router 172.23.100.4
+		router 172.23.100.6
+		address 172.23.3.0/24
+
+	network [172.23.100.8-3]
+		distance 50
+		router 172.23.100.8
+		router 172.23.100.5
+		router 172.23.100.3
+		address 172.23.2.0/24
+
+	network [172.23.100.9-2]
+		distance 60
+		router 172.23.100.9
+		router 172.23.100.7
+		router 172.23.100.8
+		address 172.23.1.0/24
+
+	network [172.23.100.10-2]
+		distance 30
+		router 172.23.100.10
+		router 172.23.100.1
+		router 172.23.100.2
+		address 172.23.6.0/24
+
+	network [192.168.15.1-10]
+		distance 20
+		router 192.168.15.1
+		router 172.23.100.10
+		address 172.23.7.0/24
+		address 192.168.101.0/24
+
+	network [192.168.15.7-24]
+		distance 10
+		router 192.168.15.7
+		router 192.168.15.10
+		router 192.168.15.11
+		router 192.168.15.1
+		address 192.168.16.0/24