doc: add Rust toolchain general install instructions

Signed-off-by: Mike McCready <66998419+MikeMcC399@users.noreply.github.com>
PR-URL: #63426
Refs: #63225
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Richard Lau <richard.lau@ibm.com>
Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>

Author: MikeMcC399

BUILDING.md

@@ -237,10 +237,23 @@ tarball and/or browse the git repository checked out at the relevant tag.
 ### Prerequisites
 
 * [A supported version of Python][Python versions] for building and testing.
-* Memory: at least 8GB of RAM is typically required when compiling with 4 parallel jobs (e.g: `make -j4`)
+* A Rust toolchain if [building Node.js with Temporal support](#building-nodejs-with-temporal-support)
+  is required (enabled by default starting in Node.js 26).
+* Memory: at least 8GB of RAM is typically required when compiling with 4 parallel jobs (e.g: `make -j4`).
 
 ### Unix and macOS
 
+Consult the official [Install Rust](https://rust-lang.org/tools/install/)
+instructions to install a Rust toolchain, required for Temporal support introduced in Node.js 25.4.0.
+Individual packages such as `rust` and `cargo` in some operating system distributions may be considered
+as an alternative, for example in CI environments.
+Consult with relevant operating system documentation to ensure that packages
+meet the minimum version specified in the
+[Building Node.js with Temporal support](#building-nodejs-with-temporal-support) section,
+as packaged versions may lag behind the `stable` version installed by the official instructions.
+Avoid mixing `rustup` together with `rust` and `cargo` package installations, due to
+potential version conflicts.
+
 #### Unix prerequisites
 
 * `gcc` and `g++` >= 13.2 or `clang` and `clang++` >= 19.1
@@ -1056,6 +1069,8 @@ requires a Rust toolchain:
 * rustc >= 1.82 (with LLVM >= 19)
 * cargo >= 1.82
 
+Refer to [Install Rust](https://rust-lang.org/tools/install/) for instructions.
+
 If `--v8-enable-temporal-support` and `--v8-disable-temporal-support` are both
 omitted, `configure.py` probes for `cargo` and `rustc`. If either is missing,
 a warning is printed and Temporal support is disabled.