update readme

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

README.md

@@ -25,26 +25,18 @@ Load a image from path './dog.jpg'.
  *Write the pipeline in simplified style:*
 
 ```python
-import towhee
+from towhee.dc2 import pipe, ops, DataCollection
 
-towhee.glob('./dog.jpg') \
-  .image_decode.cv2() \
-  .show()
-```
-
-*Write a same pipeline with explicit inputs/outputs name specifications:*
 
-```python
-import towhee
+p = (
+  pipe.input('url')
+  .map('url', 'image', ops.image_decode.cv2())
+  .output('image')
+)
 
-towhee.glob['path']('./dog.jpg') \
-  .image_decode.cv2['path', 'img']() \
-  .select['img']() \
-  .show()
+DataCollection(p('./dog.jpg')).show()
 ```
 
-
-
 <img src="./show_result.jpg" height="150px"/>
 
 
@@ -75,7 +67,7 @@ An image decode operator takes an image path as input. It decodes the image back
 
 **img**: *str*
 
-​	Image file path.
+​	Local file path or http url.