ASP design doc: remove implementation details

Will-fix: #14575

wiki/src/contribute/design/additional_software_packages.mdwn

@@ -78,8 +78,9 @@ empty. It is a oneshot service that executes
 
 `tails-additional-software install` reads `live-additional-software.conf` which
 contains a package name per line and install these packages with `apt-get`
-(using `DEBIAN_PRIORITY=critical` and the command line options `--yes` and
-`--option DPkg::Options::=--force-confold`).
+(using options prevent questions being asked to the user, see
+`install_additional_packages` and `_launch_apt_get` in
+[[!tails_gitweb config/chroot_local-includes/usr/local/sbin/tails-additional-software]]).
 
 In the beginning of the process, the user is notified through desktop
 notifications that additional software is being installed: