add object deletion chapter to index

Author: WandererFan

technical/index.md

@@ -30,6 +30,7 @@ Technical information of interest to Contributors.
 - [Creating a WorkBench](https://wiki.freecad.org/Workbench_creation)
 - The [PowerUser's hub](https://wiki.freecad.org/Power_users_hub) in the FreeCAD wiki contains good information about Python scripting and workbench creation
 - [Accessing User Preferences](./preferences.md)
+- [Controlling Object Deletion](./ObjectDeletion.md)
 - [Create a Python Binding for C++ Class](./CreatePythonBindingForCpp.md)
 - [Checklist for Adding a Feature to a Workbench in C++](./ChecklistForNewFeatureC++.md)