update readme

Signed-off-by: junjiejiangjjj <junjie.jiang@zilliz.com>

README.md

@@ -10,7 +10,7 @@
 
 ## Description
 
-An image decode operator implementation with OpenCV.
+An image decode operator implementation with OpenCV. Return BGR image.
 
 
 
@@ -20,7 +20,11 @@ An image decode operator implementation with OpenCV.
 
 ## Code Example
 
-Load a image from path './dog.jpg'. 
+Load a image from path './src_dog.jpg'. 
+
+the src picture:
+<br />
+<img src="./src_dog.jpg" height="150px"/>
 
  *Write the pipeline in simplified style:*
 
@@ -34,10 +38,11 @@ p = (
   .output('image')
 )
 
-DataCollection(p('./dog.jpg')).show()
+DataCollection(p('./src_dog.jpg')).show()
 ```
 
-<img src="./show_result.jpg" height="150px"/>
+<br />
+<img src="./dog.png" height="150px"/>
 
 
 
@@ -59,7 +64,7 @@ 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 decode operator takes an image path as input. It decodes the image back to ndarray, use BGR channel order.