docs(plugins): adds plugin page

docs/mkdocs.yml

@@ -62,6 +62,7 @@ pages:
 - ['reference/templating.md', 'Reference', 'Templating']
 - ['reference/scripting.md', 'Reference', 'Scripting']
 - ['reference/playlist.md', 'Reference', 'Playlist']
+- ['reference/plugins.md', 'Reference', 'Plugins']
 - ['reference/export_import.md', 'Reference', 'Import & Export']
 - ['reference/admin.md', 'Reference', 'Administration']
 - ['reference/http_api.md', 'Reference', 'HTTP API']

docs/sources/reference/plugins.md

+---
+page_title: Plugin guide
+page_description: Plugin guide for Grafana
+page_keywords: grafana, plugins, documentation
+---
+
+# Plugins
+
+!Plugin support for panels is only available in nightly!
+
+Adding support for all datasources and suggested panels would bloat grafana and make it impossible to maintain. Thats why we implemented a plugin system that makes it possible for anyone to develop support for a datasource or custom panel without adding it to Grafana itself.
+
+## Installing plugins
+
+Installing a plugin is very simple. Just download it and place it in the Grafana plugins folder and restart grafana.
+
+The default plugin folder is configurable under paths.plugins
+
+It's also possible to add one specific plugin by linking to its folder.
+
+```
+[plugin.mirror]
+path = /home/evil-queen/datasource-plugin-mirror
+```
+
+## Plugin implementation ##
+
+Each plugin is defined in plugin.json file in the plugin folder.
+
+Instead of massive documentation about how it works we created a reference implementation of a plugin.
+You can find each reference implementation further down on this page.
+
+## Datasource plugins
+
+Datasource have three responsibilities.
+
+ * UI for configuring its settings
+ * Datasource object that can send queries, metricqueries and healthcheck the datasource
+ * Query editor within panels
+
+https://github.com/grafana/datasource-plugin-genericdatasource
+
+## Panel plugins
+
+Panel plugins are responsible for
+
+ * UI for Panel options.
+ * Creating a directive that can render something based on datasource data.
+
+We currently dont have a reference implementation for panel plugins but you can checkout https://github.com/grafana/panel-plugin-piechart