update README

Author: twmht

README.md

@@ -6,7 +6,15 @@ WIDERFACE is a database of face bounding boxes available on http://mmlab.ie.cuhk
 ## Requirement
 scipy(v0.19.0)
 
+## Install
+
+```
+pip install python-widerface
+```
+
 ## Usage
-Please see `wider/examples/example.py` for usage
+You can use this library to extract the annotations and images from WIDERFACE.
+
+Please see [example](https://github.com/twmht/python-widerface/blob/master/wider/examples/example.py) for usage.
 
 you also need opencv and matplotlib (v2.0.0) to run the example.