doc: copyedit packages.md

Some minor adjustments, mostly moving things to present tense and
avoiding the ambiguity of _may_.

Refs: https://github.com/nodejs/node/pull/35370#issuecomment-700798044

PR-URL: https://github.com/nodejs/node/pull/35427


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Geoffrey Booth <webmaster@geoffreybooth.com>
Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michael Dawson <midawson@redhat.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>