doc: change links to use HEAD in top level docs

Change the top level docs to use HEAD in links

Signed-off-by: Michael Dawson <mdawson@devrus.com>

PR-URL: https://github.com/nodejs/node/pull/37494


Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>