update doxygen comment for EDGE_TYPE_MAP

Author: soheilshahrouz

vpr/src/draw/draw_rr.h

@@ -27,7 +27,7 @@ void draw_rr(ezgl::renderer* g);
 /// connects to. @p from_node is assumed to be a CHANX, CHANY, or IPIN.
 void draw_rr_edges(RRNodeId from_node, ezgl::renderer* g);
 
-/// Color map for edges based on {from_type, to_type}
+/// Maps (from_type, to_type) pairs to an edge type used for drawing or classification.
 inline const std::map<std::pair<e_rr_type, e_rr_type>, e_edge_type> EDGE_TYPE_MAP = {
     // Pin to pin connections
     {{e_rr_type::IPIN, e_rr_type::IPIN}, e_edge_type::PIN_TO_IPIN},