doc: add unrepresented flags docs for configure

added documentation to support usage of
advanced features of `configure` on Windows

Fixes: nodejs#17331

Author: rexagod

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

@@ -34,6 +34,11 @@ update the build and testing process on Windows.
 
 ## configure
 
+The `configure` script recognizes many CLI flags for special build formulas. Many are not represented by `vcbuild` shortcuts, and need to be passed either by:
+
+- Calling `python configure --XXX --YYY=PPPP` directly, followed by `vcbuild noprojgen`
+- Setting `set config_flags=--XXX --YYY=PPPP` before calling `vcbuild`
+
 To see the help text, run `python configure --help`. Update this file when you
 need to update the configuration process.