Add Windows build instructions to README

[TuanBC]

Added build instructions for Windows to README.md.

[wkentaro]

can't we combine the two instructions as one? (like on Windows, please replace $ with % etc.) Because shorter README is prefered.

[TuanBC]

I think it is not really that intuitive of replacing some characters. At least personally, even though I know that original command is for Linux, as I am not too familiar with using Windows powershell, it took me some searching and time to figure out too.

I wonder if a collapsible section is preferred if you want a shorter Readme?

Windows

function logSomething(something) {
  console.log('Something', something);
}