doxygen: improve

* stop transforming all // in doxygen comment /// since it doesn't work
nicely with our code base, prefer to replace // by /// when needed.

ortools/cpp/main.cpp.dox.in

@@ -3,6 +3,59 @@
 * @author Corentin "Mizux" Le Molgat <corentinl@google.com>
 */
 
+// WARNING: must keep the empty line between example otherwise doxygen has an
+// undefined behaviour...
+
+/// @namespace operations_research OR-Tools root namespace.
+
+/// @example{lineno} tsp.cc
+/// Simple TSP example.
+
+/// @example{lineno} tsp_circuit_board.cc
+/// Simple TSP example.
+
+/// @example{lineno} tsp_cities.cc
+/// Simple TSP example.
+
+/// @example{lineno} tsp_distance_matrix.cc
+/// Simple TSP example.
+
+/// @example{lineno} vrp_capacity.cc
+/// Simple VRP example.
+
+/// @example{lineno} vrp.cc
+/// Simple VRP example.
+
+/// @example{lineno} vrp_drop_nodes.cc
+/// Simple VRP example.
+
+/// @example{lineno} vrp_global_span.cc
+/// Simple VRP example.
+
+/// @example{lineno} vrp_initial_routes.cc
+/// Simple VRP example.
+
+/// @example{lineno} vrp_pickup_delivery.cc
+/// Simple VRP example.
+
+/// @example{lineno} vrp_pickup_delivery_fifo.cc
+/// Simple VRP example.
+
+/// @example{lineno} vrp_pickup_delivery_lifo.cc
+/// Simple VRP example.
+
+/// @example{lineno} vrp_resources.cc
+/// Simple VRP example.
+
+/// @example{lineno} vrp_starts_ends.cc
+/// Simple VRP example.
+
+/// @example{lineno} vrp_time_windows.cc
+/// Simple VRP example.
+
+/// @example{lineno} vrp_with_time_limit.cc
+/// Simple VRP example.
+
 /*! @mainpage OR-Tools C++ Reference
 This is the reference documentation for Google OR-Tools.