Add warnings about externaly sourced scripts (#2975)

json/nextcloudpi.json

@@ -45,6 +45,10 @@
         {
             "text": "Only Alpine: To get the username and password, run the script again inside the LXC shell.",
             "type": "warning"
+        },
+        {
+            "text": "WARNING: Installation sources scripts outside of Community Scripts repo. Please check the source before installing.",
+            "type": "warning"
         }
     ]
 }