This may help newcomers on how to easily compile bsnes

* MSYS is being recomended as another good alternative (thanks for the suggestion @jchv
* bsnes isn't bold anymore
* I changed back the link in comunity section for the same invite link already it has (and now with a fancy new button)
* Changed the I and II to more usual markdown items
* Now all the text in the README is using default MD (then rather than "-----" we have hyrarchical subtitling
* The prerequisites now is separated and better explained. Note that I'm just pointing the websites for the user get his better suited version of the compilation suite
* Git is now optional. Further instructions is given about how to download the code manually without the need of Git.
* Now the text is no longer "windows only" with instructions that can be used in Linux and MacOS too.

It's linked with the bsnes license page