doc: document os.userInfo() throwing SystemError

`os.userInfo()` throws an exception which was not documented
in environments like: `docker run --user $(id -u): $(id -g)`.

PR-URL: https://github.com/nodejs/node/pull/25724
Fixes: https://github.com/nodejs/node/issues/25714


Reviewed-By: James M Snell <jasnell@gmail.com>