notes/vpm: update information about creating qr code with configs

misc/wg-client-conf.nix

@@ -1,4 +1,3 @@
-# use nix-build -E (import <system>/misc/wg-client-conf.nix {})
 { pkgs ? import <nixpkgs> { }
 , address
 , privateKey

notes/vpn.md

@@ -8,6 +8,20 @@ wg genkey > ./private
 wg pubkey < ./private > ./public
 ```
 
+
+## Configuration
+
+Then create QR code with configuration using the following command:
+
+```sh
+nix build -f ./misc/wg-client-conf.nix \
+  --argstr address "" \
+  --argstr dns "" \
+  --argstr privateKey "$(cat private)" \
+  --argstr serverPublicKey "" \
+  --argstr serverEndpoint ""
+```
+
 # References:
 
 - https://nixos.wiki/wiki/WireGuard