added description type to class mapping

grum/descs/__init__.py

@@ -4,3 +4,10 @@ from .imgdesc import ImageDescription
 from .plotdesc import PlotDescription
 
 
+DESC_TYPES = {
+    ImageDescription.get_type(): ImageDescription,
+    PlotDescription.get_type():  PlotDescription
+}
+
+
+