Added ModelAdmin Example

Updated examples to say they are written with 3.0.x in mind and public statics should be private in 3.1.x

README.md

@@ -35,6 +35,7 @@ To move an item to another page drag the row over the respective page button and
 #### Full code Examples
 * [has_many relationship] (https://github.com/UndefinedOffset/SortableGridField/blob/master/docs/HasManyExample.md)
 * [many_many relationship] (https://github.com/UndefinedOffset/SortableGridField/blob/master/docs/ManyManyExample.md)
+* [ModelAdmin implementation] (https://github.com/UndefinedOffset/SortableGridField/blob/master/docs/ModelAdminExample.md)
 
 #### Events
 GridFieldSortableRows provides 4 "events" onBeforeGridFieldRowSort(), onAfterGridFieldRowSort(), onBeforeGridFieldPageSort() and onAfterGridFieldPageSort(). These "events" are passed a clone of the DataList used in GridFieldSortableRows, in the case of page sorting this list has a limit that shows you the current page plus/minus one object. For GridFieldSortableRows that are on ModelAdmin decendents these events are called on the ModelAdmin if they do not have a owner DataObject, if you are using GridFieldSortableRows on a GridField for a DataObject's relationship the events are called on that DataObject.

docs/HasManyExample.md

@@ -1,5 +1,6 @@
 has_many Example
 =================
+Please note this example is written with 3.0.x in mind, if you are using 3.1.x make sure you scope all static properties to private not public.
 ```php
 /*** TestPage.php ***/
 class TestPage extends Page {

docs/ManyManyExample.md

@@ -1,5 +1,6 @@
 many_many Example
 =================
+Please note this example is written with 3.0.x in mind, if you are using 3.1.x make sure you scope all static properties to private not public.
 ```php
 /*** TestPage.php ***/
 class TestPage extends Page {

docs/ModelAdminExample.md

@@ -0,0 +1,38 @@
+ModelAdmin implementation Example
+=================
+Please note this example is written with 3.0.x in mind, if you are using 3.1.x make sure you scope all static properties to private not public.
+```php
+/**** MyModelAdmin.php ****/
+class MyModelAdmin extends ModelAdmin {
+    public static $menu_title='My Model Admin';
+    public static $url_segment='my-model-admin';
+    
+    public static $managed_models=array(
+                                        'MATestObject'
+                                    );
+    
+    public function getEditForm($id = null, $fields = null) {
+        $form=parent::getEditForm($id, $fields);
+        
+        //This check is simply to ensure you are on the managed model you want adjust accordingly
+        if($this->modelClass=='MATestObject' && $gridField=$form->Fields()->dataFieldByName($this->sanitiseClassName($this->modelClass))) {
+            //This is just a precaution to ensure we got a GridField from dataFieldByName() which you should have
+            if($gridField instanceof GridField) {
+                $gridField->getConfig()->addComponent(new GridFieldSortableRows('SortOrder'));
+            }
+        }
+        
+        return $form;
+    }
+}
+
+/**** MATestObject.php ****/
+class MATestObject extends DataObject {
+    public static $db=array(
+                            'Title'=>'Varchar',
+                            'SortOrder'=>'Int'
+                        );
+    
+    public static $default_sort='SortOrder';
+}
+```