routing: Clean README.md

ortools/routing/README.md

@@ -1,6 +1,30 @@
 # Routing
 
-This folder contains utilities related to routing problems, currently only
-utilities for file formats in the
-[`parsers`](../routing/parsers)
-subfolder.
+[Vehicle Routing](http://en.wikipedia.org/wiki/Vehicle_routing) is a useful
+extension that is implemented on top of the CP solver library.
+
+## Routing solver
+
+To begin, skim:
+
+*   [../constraint_solver/routing.h](../constraint_solver/routing.h): The
+    vehicle routing library lets one model and solve generic vehicle routing
+    problems ranging from the Traveling Salesman Problem to more complex
+    problems such as the Capacitated Vehicle Routing Problem with Time Windows.
+
+### Parameters
+
+*   [../constraint_solver/routing_parameters.proto](../constraint_solver/routing_parameters.proto):
+    The Vehicle Routing solver parameters.
+*   [../constraint_solver/routing_enums.proto](../constraint_solver/routing_enums.proto):
+    Enums used to define routing parameters.
+
+### Solution
+
+*   [../constraint_solver/assignment.proto](../constraint_solver/assignment.proto):
+    Holds the solution of a Routing problem (as a special case of a CS problem).
+
+## Parsers
+
+Utilities for file formats are in the
+[`parsers`](../routing/parsers) subfolder.