Move add-site into Admin Guide.

Move Admin Guide before Developer Guide in main navigation

Author: stevepiercy

docs/install/add-site.md renamed to docs/admin-guide/add-site.md

@@ -29,6 +29,7 @@ install-pip
 :maxdepth: 1
 
 run-plone
+add-site
 configure-zope
 add-ons
 override-core

docs/admin-guide/index.md

@@ -32,8 +32,8 @@ Read the [documentation for the previous version, Plone 5](https://5.docs.plone.
 
 overview/index
 install/index
-developer-guide/index
 admin-guide/index
+developer-guide/index
 deployment/index
 volto/index
 classic-ui/index