Add pre-install script to the notes section of template.

template/apps/dashy.json

@@ -20,6 +20,7 @@
 	"logo": "https://raw.githubusercontent.com/pi-hosted/pi-hosted/master/images/dashy.png",
 	"name": "Dashy",
 	"officialDoc": "https://dashy.to/docs/quick-start",
+        "preInstallScript": "install_dashy.sh",
 	"platform": "linux",
 	"ports": [
 		"9100:80/tcp"