doc: add note regarding pushing release tags

Tags shouldn't be pushed unless the remainder of release steps are able
to be completed.

PR-URL: https://github.com/nodejs/node/pull/25569


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Shelley Vohr <codebytere@gmail.com>
Reviewed-By: Beth Griggs <Bethany.Griggs@uk.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>