doc: update boxstarter README

PR-URL: #53785
Reviewed-By: Ulises Gascón <ulisesgascongonzalez@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

tools/bootstrap/README.md

@@ -1,3 +1,2 @@
-See the main project
-[BUILDING.md](../../BUILDING.md#option-2-automated-install-with-boxstarter)
-for details on how to use this script.
+Refer to [BUILDING.md](../../BUILDING.md#option-2-automated-install-with-boxstarter) for
+instructions on how to build Node.js with boxstarter.