add plugin docs

docs/dev/plugin.md

@@ -0,0 +1,51 @@
+---
+layout: default
+title: Plugins
+permalink: /dev/plugins
+nav_order: 2
+parent: Hacking
+---
+
+## Plugins
+Since **v.1.2.2** you can write your own plugin that react to event related action (create,update,delete).
+
+> info "What this is useful for?"
+> - Do you want to create a post in your wordpress website each time an event is published? [hint](http://wp-api.org/node-wpapi/using-the-client/#creating-posts)
+> - Do you want to send a summary notification of daily events via mail?
+> - Notify a telegram group or share via twitter?  
+>  
+> [**<u>Please share your plugins or your needs</u>**](/contacts)
+
+Plugins should be inside `./plugins` directory, this is an example:
+
+```js
+const plugin = {
+  gancio: null,
+  load (gancio) {
+    console.error('Plugin GancioPluginExample loaded!')
+    plugin.gancio = gancio
+  },
+
+  onEventCreate (event) {
+    const eventLink = `${plugin.gancio.settings.baseurl}/event/${event.slug}`
+    if (!event.is_visible) {
+      console.error(`Unconfirmed event created: ${event.title} / ${eventLink}`)
+    } else {
+      console.error(`Event created: ${event.title} / ${eventLink}`)
+    }
+  },
+
+  onEventUpdate (event) {
+    console.error(`Event "${event.title}" updated`)
+  },
+
+  onEventDelete (event) {
+    console.error(`Event "${event.title}" deleted`)
+  }
+}
+
+
+module.exports = plugin
+```
+
+