Override default arch sysctl config

Ours was 00-; Arch's is 10-; as a result Arch's config is taking
precedence over ours!

This mostly doesn't matter except for `fs.inotify.max_user_instances`,
which is set in both. Because Arch's file wins, the value is currently
stuck at 1024 instead of the 8192 value we intended.

mkosi.extra/usr/lib/sysctl.d/11-kde-linux-default.conf

@@ -2,6 +2,8 @@
 # SPDX-FileCopyrightText: 2025 Nate Graham <nate@kde.org>
 # SPDX-FileCopyrightText: 2025 Thomas Duckworth <tduck@filotimoproject.org>
 
+# Numbered 11- to take precedence over the default Arch config, which is 10-
+
 # With fast RAM-backed swap (zram), tell the kernel it's faster than I/O so it
 # doesn't use slower file pages as often
 vm.swappiness = 180