Build-image: Document Rust support and move out of alpha

[vbrown608]

Today we added rustup to our default build image (https://github.com/netlify/build-image/pull/477). Once we see that it's working well, we should promote the change.

[kalwalt]

Hi @vbrown608, there is a documentation or some example available? I'm a kind of novice with Rust and i'd like to try some little Rust project with Netlify.

[mraerino]

i see these as things to fix before GA:

• https://github.com/netlify/build-image/issues/508
• https://github.com/netlify/build-image/issues/505

apart from these it's working fine for our team internally

[calavera]

I opened a PR to address both: https://github.com/netlify/build-image/pull/521

[rstavchansky]

Hi @vbrown608, there is a documentation or some example available? I'm a kind of novice with Rust and i'd like to try some little Rust project with Netlify.

@kalwalt We've added basic documentation for how to set up Rust with Netlify. You can find it it our technical docs under Manage dependencies.

[mraerino]

a user encountered a problem with the caching when installting a rust crate without a Cargo.toml: https://github.com/netlify/binrc/pull/29#issuecomment-761044840

[kalwalt]

@rstavchansky thank you very much! This is awesome!🙂👍🎉