add doc for ajax_update (#2728)

* add documentation for ajax_update
Fixes #2401

Author: samialfattani

doc/introduction.rst

@@ -256,8 +256,11 @@ For a faster editing experience, enable **inline editing** in the list view::
 
     column_editable_list = ['name', 'last_name']
 
-Or, have the add & edit forms display inside a **modal window** on the list page, instead of
-the dedicated *create* & *edit* pages::
+Editable_list is converts each column into Ajax form so that you can edit & save the new value
+in same row. see the API docs :meth:`~flask_admin.model.BaseModelView.ajax_update` for Ajax example.
+
+Another way of inline editing without losing the current context, have the add & edit forms display
+inside a **modal window** on the list page, instead of the dedicated *create* & *edit* pages::
 
     create_modal = True
     edit_modal = True

flask_admin/model/base.py

@@ -2684,12 +2684,33 @@ def ajax_lookup(self) -> T_RESPONSE:
     @expose("/ajax/update/", methods=("POST",))
     def ajax_update(self) -> None | tuple[str, int] | str:
         """
-        Edits a single column of a record in list view.
+        Edits a single column of a record in list view. Usually used with
+        `column_editable_list` that integrates with the x-editable library.
+
+        .. code-block:: javascript
+
+            // you can use jQuery to make ajax calls like this:
+
+            $.ajax({
+                url: '/admin/<your_model_view_endpoint>/ajax/update/',
+                type: 'POST',
+                data: {
+                    "list_form_pk" : "<primary_key_value>",
+                    "<column_name>": "<new_value>"
+                },
+                success: function(response) {
+                    // handle success
+                },
+                error: function(response) {
+                    // handle error
+                }
+            });
+
         """
         if not self.column_editable_list:
             abort(404)
 
-        form = self.list_form()
+        form = self.list_form()  # returns a form of all fields
 
         # prevent validation issues due to submitting a single field
         # delete all fields except the submitted fields and csrf token