Chapter convolutional neural networks/why conv (#902)
Chapter convolutional neural networks/why conv (#902)

* fix errors in 6.1. From FC Layers to Convolutions

* fix errors in 6.1.1. Invariance

* fix errors in 6.1.2. Constraining the MLP

* fix errors in 6.1.3. Convolutions

* Update why-conv.md

* polish

Co-authored-by: goldmermaid <fcb00cecbf879d17a80f4ce26a389eda39da7621@berkeley.edu>
mli/gluon-tutorials-zh,d2l-ai/d2l-zh,mli/gluon-tutorials-zh,mli/gluon-tutorials-zh,d2l-ai/d2l-zh,mli/gluon-tutorials-zh,d2l-ai/d2l-zh