moving extension dev overview

doc/development/index.rst

@@ -10,6 +10,7 @@ wish to use Sphinx with existing extensions, refer to :doc:`/usage/index`.
 .. toctree::
    :maxdepth: 2
 
+   overview
    tutorials/index
    builders
 

doc/development/tutorials/index.rst

@@ -5,10 +5,6 @@ Extension tutorials
 
 Refer to the following tutorials to get started with extension development.
 
-.. toctree::
-   :caption: General extension tutorials
-
-   overview
 
 .. toctree::
    :caption: Directive tutorials