Add section 'Getting Started' to README.md

[henry40408]

No description provided.

[weihanglo]

@henry40408
I prefer to keep our main README concise and not to mention contribution details there.
Our goal is providing tutorials about common algorithms in Rust. Hence, I think separating contribution details into different document is more appropriate.

Would you mind move these great resources into another file?

[henry40408]

@weihanglo No, but how we call that file? I suggest GETTING_STARTED.md. By the way, I insist to put a link to the file in README.md. We can't expect everyone to have Rust already installed on their laptop.

[weihanglo]

I am fine with GETTING_STARTED.md. We can include the link to GETTING_STARTED.md instead of the whole details.

[henry40408]

@weihanglo updated, please review

[weihanglo]

Maybe override directory toolchain would be a better choice.

rustup override set stable

[weihanglo]

I'll merge this first. We can send following PRs later.