Padding and Strides

http://d2l.ai/chapter_convolutional-neural-networks/padding-and-strides.html

Minor formatting in section: 6.3. Padding and Stride,

2nd phrase double check and change :numref: sec_conv_layer

Thanks. Now it’s fixed. See comments in https://github.com/d2l-ai/d2l-en/issues/1448