refactor: move nixos-manual to reference/ + graphifyignore

reference/nixos-manual/configuration/ad-hoc-network-config.section.md

@@ -0,0 +1,14 @@
+# Ad-Hoc Configuration {#ad-hoc-network-config}
+
+You can use [](#opt-networking.localCommands) to
+specify shell commands to be run at the end of `network-setup.service`. This
+is useful for doing network configuration not covered by the existing NixOS
+modules. For instance, to statically configure an IPv6 address:
+
+```nix
+{
+  networking.localCommands = ''
+    ip -6 addr add 2001:610:685:1::1/64 dev eth0
+  '';
+}
+```