doc: update to adding listens on SIGUSR1

Updated the doc/api/process.md documentation to reflect that
listening on SIGUSR1 could impact the debugger.

Fixes: https://github.com/nodejs/node/issues/19619

PR-URL: https://github.com/nodejs/node/pull/19709


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>