Add grad-cam example

Author: koki0702

README.md

@@ -67,7 +67,7 @@ DeZeroの他の実装例は[examples](/examples)にあります。
 
 [<img src="https://raw.githubusercontent.com/oreilly-japan/deep-learning-from-scratch-3/images/gan.gif" height="175"/>](/examples/gan.py)[<img src="https://raw.githubusercontent.com/oreilly-japan/deep-learning-from-scratch-3/images/vae.png" height="175"/>](/examples/vae.py)[<img src="https://raw.githubusercontent.com/oreilly-japan/deep-learning-from-scratch-3/images/pythonista.png" height="175"/>](https://github.com/oreilly-japan/deep-learning-from-scratch-3/wiki/DeZero%E3%82%92iPhone%E3%81%A7%E5%8B%95%E3%81%8B%E3%81%99)
 
-[<img src="https://raw.githubusercontent.com/oreilly-japan/deep-learning-from-scratch-3/images/style_transfer.png" height="175"/>](/examples/style_transfer.py)
+[<img src="https://raw.githubusercontent.com/oreilly-japan/deep-learning-from-scratch-3/images/style_transfer.png" height="175"/>](/examples/style_transfer.py)[<img src="https://raw.githubusercontent.com/oreilly-japan/deep-learning-from-scratch-3/images/grad_cam.png" height="175"/>](/examples/grad_cam.py)
 
 ## 正誤表