tools: add links to the stability index reference

This modifies the script that generates the docs
to create a static link from each Stability Index callout bar to
the Stability Index explanations in documentation.html.

PR-URL: https://github.com/nodejs/node/pull/11664


Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>