Update README

Signed-off-by: Jael Gu <mengjia.gu@zilliz.com>

README.md

@@ -29,8 +29,8 @@ Create the operator via the following factory method
 
 ## Interface
 
-An image decode operator takes an image path as input. It decodes the image back to ndarray.
-
+An image embedding operator takes an image in ndarray as input.
+It uses the pre-trained model specified by model name to generate an image embedding in ndarray.
 
 
 **Parameters:**