Documentation skeleton (#1617)

* Documentation skeleton

* Added ADR list and more

* rm material theme

* Update mkdocs.yml

* Add docs TOC

* Work for plain MD and mkdocs

* Update mkdocs.yml

* Restructuring

* Added roadmap

* Add reference APIs

* move publishing

docs/plugins/index.md

@@ -0,0 +1,26 @@
+# Plugins
+
+Backstage is a single-page application composed of a set of plugins.
+
+Our goal for the plugin ecosystem is that the definition of a plugin is flexible
+enough to allow you to expose pretty much any kind of infrastructure or software
+development tool as a plugin in Backstage. By following strong
+[design guidelines](https://github.com/spotify/backstage/blob/master/docs/design.md)
+we ensure the the overall user experience stays consistent between plugins.
+
+![plugin](../docs/getting-started/my-plugin_screenshot.png)
+
+## Creating a plugin
+
+To create a plugin, follow the steps outlined
+[here](https://github.com/spotify/backstage/blob/master/docs/getting-started/create-a-plugin.md).
+
+## Suggesting a plugin
+
+If you start developing a plugin that you aim to release as open source, we
+suggest that you create a new
+[new Issue](https://github.com/spotify/backstage/issues/new?template=plugin_template.md).
+This helps the community know what plugins are in development.
+
+You can also use this process if you have an idea for a good plugin but you hope
+that someone else will pick up the work.