add CR between mailing lists

Former-commit-id: 5d5284f8ea

README.md

@@ -16,6 +16,7 @@ OpenDroneMap is a toolchain for processing raw civilian UAS imagery to other use
 So far, it does Point Clouds, Digital Surface Models, Textured Digital Surface Models, and Orthorectified Imagery.
 
 Users' mailing list: http://lists.osgeo.org/cgi-bin/mailman/listinfo/opendronemap-users
+
 Developer's mailing list: http://lists.osgeo.org/cgi-bin/mailman/listinfo/opendronemap-dev