add medialink in manifest

CloudronManifest.json

@@ -19,7 +19,7 @@
   },
   "tags": [ "apache", "php", "mysql", "linux" ],
   "developmentMode": false,
-  "mediaLinks": [],
+  "mediaLinks": [ "https://raw.githubusercontent.com/cloudron-io/lamp-app/master/medialinks/medialink_0.jpg" ],
   "changelog": "file://CHANGELOG",
   "minBoxVersion": "0.13.3"
 }