doc: clarify http2.connect authority details

Fixes: https://github.com/nodejs/node/issues/31827

PR-URL: https://github.com/nodejs/node/pull/31828


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Signed-off-by: James M Snell <jasnell@gmail.com>