README.md without prompts for easy copying

[stappersg]

Removed several prompts, $ and > , for convenient copy and paste.

When clicking on the copy symbol while hovering over the ``` text block gets the $ also on the clipboard paste buffer.

For people who don't use webbrowser with JavaScript enabled is selecting the two lines git clone https://github.com/rust-lang/rust.git cd rust much easier as avoiding $ from $ git clone https://github.com/rust-lang/rust.git $ cd rust

Most ``` blocks are now consistent with the very first ./x.py [flags]

[stappersg]

This dangling merge request prevents me to github fork rustlang/rust. And so blocking that development.

[MabezDev]

Thanks for the PR, but I've removed the instructions completely, and now direct users towards the upstream instructions.