doc: add guide on maintaining build files

PR-URL: #16975
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Rod Vagg <rod@vagg.org>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>

doc/guides/maintaining-the-build-files.md

@@ -0,0 +1,52 @@
+# Maintaining the Build files
+
+This document explains how to maintain the build files in the codebase.
+
+## Overview
+
+On how to build the Node.js core, see [Building Node.js](../../BUILDING.md).
+
+There are three main build files that may be directly run when building Node.js:
+
+- `configure`: A Python 2 script that detects system capabilities and runs
+  [GYP][]. It generates `config.gypi` which includes parameters used by GYP to
+  create platform-dependent build files. Its output is usually in one of these
+  formats: Makefile, MSbuild, ninja, or XCode project files. (Note: the main
+  Makefile mentioned below is maintained separately by humans). For a detailed
+  guide on this script, see [configure](#configure).
+- `vcbuild.bat`: A Windows Batch Script that locates build tools, provides a
+  subset of the targets avilable in the [Makefile](#makefile), and a few targets
+  of its own. For a detailed guide on this script, see
+  [vcbuild.bat](#vcbuild.bat).
+- `Makefile`: A Makefile that can be run with GNU Make. It provides a set of
+  targets that build and test the Node.js binary, produce releases and
+  documentation, and interact with the CI to run benchmarks or tests. For a
+  detailed guide on this file, see [Makefile](#makefile).
+
+On Windows `vcbuild.bat` runs [configure](#configure) before building the
+Node.js binary, on other systems `configure` must be run manually before running
+`make` on the `Makefile`.
+
+## vcbuild.bat
+
+To see the help text, run `.\vcbuild help`. Update this file when you need to
+update the build and testing process on Windows.
+
+## configure
+
+To see the help text, run `python configure --help`. Update this file when you
+need to update the configuration process.
+
+## Makefile
+
+To see the help text, run `make help`. This file is not generated, it is
+maintained by humans. Note that this is not usually run on Windows, where
+[vcbuild.bat](#vcbuild.bat) is used instead.
+
+### Options
+
+- `-j <n>`: number of threads used to build the binary. Note that on the non-ci
+  targets, the parallel tests will take up all the available cores, regardless
+  of this option.
+
+[GYP]: https://gyp.gsrc.io/docs/UserDocumentation.md