translate _chapters_jp/neural_networks.md about ml4a.github.io

[genekogan]

凄い !

[micuat]

@genekogan @kynd how can we translate the demo script?
https://github.com/ml4a/ml4a.github.io/blob/master/demos/demos/simple_forward_pass.js

It will be great if the texts are loaded from asset files instead of hardcoding and an asset file will be loaded according to the language preset (I know it's easy to propose but needs effort to implement it!)

[micuat]

@kynd I finished draft of chapter 2. could you take a look on google docs when you have time?

[genekogan]

@micuat yeah this would be a great idea ... i think the right way to do this would be through putting it as variables in https://raw.githubusercontent.com/ml4a/ml4a.github.io/master/_demos/simple_forward_pass.md and loading from there. i can take a look at this at some point, maybe not this week though.