doc: document "Resume Build" limitation

Compiled binaries for fanned CI builds on Windows and ARM are only kept
for seven days.

PR-URL: https://github.com/nodejs/node/pull/30604


Reviewed-By: Beth Griggs <Bethany.Griggs@uk.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>