add some info about plugins

README

@@ -1429,6 +1429,51 @@ notify third-party servers of updates.
 notify: an array of URLs for ping endpoints. Default is the empty
         array (no notification).
 
+Plugins
+=======
+
+Beginning with the 0.7.x branch, Laconica has supported a simple but
+powerful plugin architecture. Important events in the code are named,
+like 'StartNoticeSave', and other software can register interest
+in those events. When the events happen, the other software is called
+and has a choice of accepting or rejecting the events.
+
+In the simplest case, you can add a function to config.php and use the
+Event::addHandler() function to hook an event:
+
+    function AddGoogleLink($action)
+    {
+        $action->menuItem('http://www.google.com/', _('Google'), _('Search engine'));
+        return true;
+    }
+
+    Event::addHandler('EndPrimaryNav', 'AddGoogleLink');
+
+This adds a menu item to the end of the main navigation menu. You can
+see the list of existing events, and parameters that handlers must
+implement, in EVENTS.txt.
+
+The Plugin class in lib/plugin.php makes it easier to write more
+complex plugins. Sub-classes can just create methods named
+'onEventName', where 'EventName' is the name of the event (case
+matters!). These methods will be automatically registered as event
+handlers by the Plugin constructor (which you must call from your own
+class's constructor).
+
+Several example plugins are included in the plugins/ directory. You
+can enable a plugin with the following line in config.php:
+
+    addPlugin('Example', array('param1' => 'value1',
+                               'param2' => 'value2'));
+
+This will look for and load files named 'ExamplePlugin.php' or
+'Example/ExamplePlugin.php' either in the plugins/ directory (for
+plugins that ship with Laconica) or in the local/ directory (for
+plugins you write yourself or that you get from somewhere else) or
+local/plugins/.
+
+Plugins are documented in their own directories.
+
 Troubleshooting
 ===============