add usage description

README.md

@@ -7,3 +7,11 @@ https://pannellum.org/
 
 python panoconfig.py input.txt -o index.htm
 
+put index.htm in panellum folder together with images inside images/ folder.
+
+## input config file format
+x,y,z,id,filename,angleoffset
+
+xyz have to be a consistent unit
+angleoffset is positive if center of image is rotated ccw
+