add zsh completions

Makefile

@@ -10,10 +10,12 @@ install:
 	install -Dm 644 LICENSE -t "$(PREFIX)/share/doc/diyvpn"
 	install -dm 755 "$(PREFIX)/lib/systemd/user-generators"
 	ln -snf ../../diyvpn/diyvpn.sh "$(PREFIX)/lib/systemd/user-generators/diyvpn"
+	install -Dm 644 _diyvpnctl "$(PREFIX)/share/zsh/site-functions/_diyvpnctl"
 
 .PHONY: uninstall
 uninstall:
 	rm -rf "$(PREFIX)/lib/diyvpn" \
 		"$(PREFIX)/bin/diyvpnctl" \
 		"$(PREFIX)/share/doc/diyvpn" \
-		"$(PREFIX)/lib/systemd/user-generators/diyvpn"
+		"$(PREFIX)/lib/systemd/user-generators/diyvpn" \
+		"$(PREFIX)/share/zsh/site-functions/_diyvpnctl"

_diyvpnctl

@@ -0,0 +1,13 @@
+#compdef diyvpnctl
+
+_diyvpnctl_main() {
+  local -a commands
+  commands=(
+    'add:Configure a new VPN server'
+    'list:List configured VPN servers'
+  )
+
+  _describe 'command' commands
+}
+
+_diyvpnctl_main