add sd_notify support

mount-daemon/wireguard-mount.c

@@ -1,6 +1,7 @@
 #include <sys/mount.h>
 #include <unistd.h>
 #include <stdio.h>
+#include <systemd/sd-daemon.h>
 
 int main() {
     char mount_path[32] = {0};
@@ -11,6 +12,7 @@ int main() {
         perror("Error");
         return 1;
     }
+    sd_notify(0, "READY=1");
     while(1) {
         sleep(10);
     }