Update README.md

[Taky0nDon]

Clarified the set up process for Windows users, since simply copy and pasting the echo command in Running Locally will result in invalid json on windows. I also added a sentence to the Building Binaries section stating that this step is unnecessary if you just want to run the game.

I struggled trying to set up emscripten thinking building the binaries was a necessary step, so I tried to make it clearer that the game could be ran as is simply by following the instructions in the next section. I did have to modify the creation of web.json, since I produced invalid json until I tried the command without the outer '.