docs: point dev checks to just (#7673)

Update install and contributing guides to use the root justfile helpers
(`just fmt`, `just fix -p <crate>`, and targeted tests) instead of the
older cargo fmt/clippy/test instructions that have been in place since
459363e17b. This matches the justfile relocation to the repo root in
952d6c946 and the current lint/test workflow for CI (see
`.github/workflows/rust-ci.yml`).

docs/install.md

@@ -24,6 +24,10 @@ curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
 source "$HOME/.cargo/env"
 rustup component add rustfmt
 rustup component add clippy
+# Install helper tools used by the workspace justfile:
+cargo install just
+# Optional: install nextest for the `just test` helper (or use `cargo test --all-features` as a fallback)
+cargo install cargo-nextest
 
 # Build Codex.
 cargo build
@@ -31,10 +35,14 @@ cargo build
 # Launch the TUI with a sample prompt.
 cargo run --bin codex -- "explain this codebase to me"
 
-# After making changes, ensure the code is clean.
-cargo fmt -- --config imports_granularity=Item
-cargo clippy --tests
+# After making changes, use the root justfile helpers (they default to codex-rs):
+just fmt
+just fix -p <crate-you-touched>
 
-# Run the tests.
-cargo test
+# Run the relevant tests (project-specific is fastest), for example:
+cargo test -p codex-tui
+# If you have cargo-nextest installed, `just test` runs the full suite:
+just test
+# Otherwise, fall back to:
+cargo test --all-features
 ```