Rust rules documentation issues

[The documentation for `rust_binary`](https://buck2.build/docs/api/rules/#rust_binary) says:

> For more examples, check out our [integration tests](https://github.com/facebook/buck/tree/dev/test/com/facebook/buck/rust/testdata/).

That link is broken and points to the Buck repo, not Buck 2.

Additionally it doesn't say how to integrate with Cargo. There seems to be [some `autocargo` parameter](https://github.com/facebook/buck2/blob/981d4b47f090f8c03eafc068fc244e3d832b22cf/integrations/rust-project/BUCK#L12) which isn't documented, and also [this `rust-project` tool](https://github.com/facebook/buck2/tree/main/integrations/rust-project) which isn't mentioned.

Start with the rust_binary documentation at docs/api/rules and compare its integration-test link with the Buck 2 repository. Read integrations/rust-project/BUCK, especially the autocargo parameter, and the integrations/rust-project tool directory. Done means the broken link is corrected and the documented Cargo integration covers the referenced pieces.

Written by the indexing model from the issue text.