added instructions and sample output

[SVN r12114]

example/push-relabel-eg.cpp

@@ -27,6 +27,37 @@
 #include <boost/graph/push_relabel_max_flow.hpp>
 #include <boost/graph/adjacency_list.hpp>
 #include <boost/graph/read_dimacs.hpp>
+
+// Use a DIMACS network flow file as stdin.
+// push-relabel-eg < max_flow.dat
+//
+// Sample output:
+//  c  The total flow:
+//  s 13
+//
+//  c flow values:
+//  f 0 6 3
+//  f 0 1 0
+//  f 0 2 10
+//  f 1 5 1
+//  f 1 0 0
+//  f 1 3 0
+//  f 2 4 4
+//  f 2 3 6
+//  f 2 0 0
+//  f 3 7 5
+//  f 3 2 0
+//  f 3 1 1
+//  f 4 5 4
+//  f 4 6 0
+//  f 5 4 0
+//  f 5 7 5
+//  f 6 7 3
+//  f 6 4 0
+//  f 7 6 0
+//  f 7 5 0
+
+
 int
 main()
 {