DOCS: Add navbar_persistent to overview layout (#1849)

Fixes #1782

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Daniel McCloy <[email protected]>

Author: 3 people

docs/user_guide/layout.rst

@@ -50,23 +50,31 @@ For  complete reference of the existing option please see :ref:`the last section
 
             .. grid-item::
                 :padding: 2
-                :columns: 3
+                :columns: 2
 
                 Logo
 
                 ``navbar_start``
 
             .. grid-item::
                 :padding: 2
-                :columns: 6
+                :columns: 4
 
                 Section links
 
                 ``navbar_center``
 
             .. grid-item::
                 :padding: 2
-                :columns: 3
+                :columns: 4
+
+                Persistent components
+
+                ``navbar_persistent``
+
+            .. grid-item::
+                :padding: 2
+                :columns: 2
 
                 Components