Add missing selector property for layout field, fixes #2180

Author: texnixe

content/docs/3_reference/3_panel/3_fields/0_layout/reference-article.txt

@@ -66,6 +66,29 @@ The layout field supports up to 12 columns and all are listed below.
 - `11/12`
 - `12/12`
 
+<since v="4.0.0">
+
+## Customizing the selector
+
+You can customize the size and number of columns in the layout selector to account for the number of different layouts you have defined via the `layouts` property.
+
+
+```yaml
+fields:
+  layout:
+    type: layout
+    layouts:
+      # ...
+    selector:
+      size: huge
+      columns: 6
+```
+
+Available sizes: `small`, `medium` (default), `large`, `huge`
+Default columns: 3
+
+</since>
+
 ## Fieldsets
 
 The layout field also accepts the `fieldsets` option from the blocks field to control blocks in columns.