Update README

Signed-off-by: shiyu22 <shiyu.chen@zilliz.com>

README.md

@@ -1,4 +1,4 @@
-# Transform Image Operator
+# Image Preprocessing Operator
 
 Authors: derekdqc, shiyu22
 
@@ -14,23 +14,25 @@ In computer vision (CV) directions, image transformations are usually an indispe
 
 **Args:**
 
-​	size(`int`):
-
-​		The size of the output image.
+- size:
+  - the size of the output image
+  - supported types: `int`
 
 `__call__(self, img: Union[np.ndarray, Image.Image, torch.Tensor, str])`
 
 **Args:**
 
-​	img(`Union[np.ndarray, Image.Image, torch.Tensor, str]`):
-
-​		Original image data, the type can be np.ndarry, PIL.image, or str path of the image.
+- img:
+  - the input image to be processed
+  - supported type: `np.ndarry` or ` PIL.image` or `str` (path of the image)
 
 **Returns:**
 
-​	(`Tuple[('img_transformed', torch.Tensor)]`)
+The Operator returns a tuple `Tuple[('img_transformed', torch.Tensor)]` containing following fields:
 
-​		The tensor of the transformed image.
+- img_transformed:
+  - the tensor of the transformed image
+  - data type: `torch.Tensor`
 
 ## Requirements
 
@@ -45,3 +47,4 @@ The `towhee/transform-image` Operator is used for image transformation and is an
 ## Reference
 
 - https://pytorch.org/vision/stable/transforms.html
+