Improve Automatic Actions plugin api

doc/plugin-registration.markdown

@@ -138,40 +138,3 @@ $this->on('app.bootstrap', function($container) {
 
 - The first argument is the event name
 - The second argument is a PHP callable function (closure or class method)
-
-Extend Automatic Actions
-------------------------
-
-To define a new automatic action with a plugin, you just need to call the method `extendActions()` from the class `Kanboard\Model\Action`, here an example:
-
-```php
-<?php
-
-namespace Kanboard\Plugin\AutomaticAction;
-
-use Kanboard\Core\Plugin\Base;
-
-class Plugin extends Base
-{
-    public function initialize()
-    {
-        $this->action->extendActions(
-            '\Kanboard\Plugin\AutomaticAction\Action\DoSomething', // Use absolute namespace
-            t('Do something when the task color change')
-        );
-    }
-}
-```
-
-- The first argument of the method `extendActions()` is the action class with the complete namespace path. **The namespace path must starts with a backslash** otherwise Kanboard will not be able to load your class.
-- The second argument is the description of your automatic action.
-
-The automatic action class must inherit from the class `Kanboard\Action\Base` and implements all abstract methods:
-
-- `getCompatibleEvents()`
-- `getActionRequiredParameters()`
-- `getEventRequiredParameters()`
-- `doAction(array $data)`
-- `hasRequiredCondition(array $data)`
-
-For more details you should take a look to existing automatic actions or this [plugin example](https://github.com/kanboard/plugin-example-automatic-action).