updated documentation with vref and costmap

rosbuild/README.txt

@@ -244,6 +244,19 @@ SUBSCRIBED TOPICS:
   tf (tf/tfMessage) -- TF data used by the TF libraries to, e.g.,
   obtain robot current pose
 
+  navigator/param/vref (std_msgs/Float64) -- reference speed to be
+  used in navigation (for fixed goal only)
+
+  navigator/costmap (nav_msgs/OccupancyGrid) -- costmap for fixed goal
+  navigation; each time a message is received, the motion is replanned
+  (via FMM); note that thid occgrid aims at compatibility with
+  navigation stack, that is: (1) the cell range is 0-100 where 0 means
+  no cost and 100 means obstacle, and (2) the data is a flattened
+  row-major array with rows arranjed with increasing values of
+  y. Limitations: i) the scale has to match the map one, ii) frame_id
+  is assumed /map, and iii) orientation is ignored.
+
+
 Note that other topics are dynamically subscribed for specific modes,
 namely velocity tracking (geometry_msgs/TwistStamped) and heading
 control (std_msgs/Float64).