docs: rust-analyzer integration

[lucascolley]

The main steps needed to make pixi work with rust-analyzer seem to be:

1. add rust-src into your development environment (e.g. chore: add rust-src dependency rattler-build#1374)
2. tell rust-analyzer where to find the binaries in your pixi env, e.g. by adding the following to VSCode settings:

"rust-analyzer.server.extraEnv": {
    "PATH": "/path/to/project/.pixi/envs/default/bin:$PATH"
}

Perhaps this could be a new page under https://pixi.sh/latest/ide_integration/, maybe with a note in https://pixi.sh/latest/tutorials/rust/ linking to it?

[Hofer-Julian]

You should be able to generalize the setting with ${workspaceFolder}:

"rust-analyzer.server.extraEnv": {
    "PATH": "${workspaceFolder}/.pixi/envs/default/bin:$PATH"
}