document bootstrap tool module

Signed-off-by: onur-ozkan <work@onurozkan.dev>

Author: onur-ozkan

src/bootstrap/src/core/build_steps/compile.rs

@@ -840,7 +840,7 @@ fn cp_rustc_component_to_ci_sysroot(builder: &Builder<'_>, sysroot: &Path, conte
 /// Low-level implementation of the compiler's compilation process.
 ///
 /// DO NOT `pub` the fields of this type and AVOID using it anywhere
-/// unless it’s in the `Assemble` step.
+/// unless it's in the `Assemble` step.
 ///
 /// If you want to build a compiler for a specific stage and target, use
 /// `Builder::compiler` instead.

src/bootstrap/src/core/build_steps/tool.rs

@@ -1,3 +1,14 @@
+//! This module handles building and managing various tools in bootstrap
+//! build system.
+//!
+//! **What It Does**
+//! - Defines how tools are built, configured and installed.
+//! - Manages tool dependencies and build steps.
+//! - Copies built tool binaries to the correct locations.
+//!
+//! Each tool **MUST** utilize `ToolBuild` inside their `Step` logic and
+//! they should never prepare `cargo` invocations manually.
+
 use std::path::PathBuf;
 use std::{env, fs};