16349 add warning to custom script docs

Author: arthanson

docs/customization/custom-scripts.md

@@ -17,6 +17,9 @@ They can also be used as a mechanism for validating the integrity of data within
 
 Custom scripts are Python code which exists outside the NetBox code base, so they can be updated and changed without interfering with the core NetBox installation. And because they're completely custom, there is no inherent limitation on what a script can accomplish.
 
+!!! danger "Only install trusted scripts"
+    Custom scripts have unrestricted access to change anything in the databse and are inherently unsafe and should only be installed and run from trusted sources.  You should also review and set permissions for who can run scripts if the script can modify any data.
+
 ## Writing Custom Scripts
 
 All custom scripts must inherit from the `extras.scripts.Script` base class. This class provides the functionality necessary to generate forms and log activity.