Added comments about the vehicle detectors.

README.md

@@ -62,3 +62,12 @@ This repository contains trained models created by me (Davis King).  They are pr
    Also note that this model file is designed for use with dlib's HOG face detector.  That is, it expects the bounding
    boxes from the face detector to be aligned a certain way, the way dlib's HOG face detector does it.  It won't work
    as well when used with a face detector that produces differently aligned boxes.
+
+* mmod_rear_end_vehicle_detector.dat.bz2
+
+  This model is trained on the [dlib rear end vehicles dataset](http://dlib.net/files/data/dlib_rear_end_vehicles_v1.tar).  The dataset contains images from vehicle dashcams which I manually annotated using dlib's imglab tool.
+
+* mmod_front_and_rear_end_vehicle_detector.dat.bz2
+
+  This model is trained on the [dlib front and rear end vehicles dataset](http://dlib.net/files/data/dlib_front_and_rear_vehicles_v1.tar).  The dataset contains images from vehicle dashcams which I manually annotated using dlib's imglab tool.
+