Added Face Detection tutorial using OpenCV

Author: sayands

README.md

@@ -325,6 +325,7 @@ To get started, simply fork this repo. Please refer to [CONTRIBUTING.md](CONTRIB
 
 ### OpenCV:
 * [Build A Document Scanner](https://www.pyimagesearch.com/2014/09/01/build-kick-ass-mobile-document-scanner-just-5-minutes/)
+* [Build A Face Detector using OpenCV and Deep Learning](https://www.pyimagesearch.com/2018/02/26/face-detection-with-opencv-and-deep-learning/)
 
 ### Deep Learning: