[Docs] Various fixes (#2136)

* [Docs] Various fixes

* More fixes

* Fix ADRs

* Typo

docs/plugins/plugin-development.md

@@ -1,6 +1,6 @@
 ---
 id: plugin-development
-title: Plugin Development in Backstage
+title: Plugin Development
 ---
 
 Backstage plugins provide features to a Backstage App.
@@ -10,28 +10,12 @@ type of content. Plugins all use a common set of platform APIs and reusable UI
 components. Plugins can fetch data from external sources using the regular
 browser APIs or by depending on external modules to do the work.
 
-<!-- MOVED TO create-a-plugin.md ## Creating a new plugin
-On your command line, invoke the `backstage-cli` to create a new plugin:
-```bash
-yarn create-plugin
-```
-
-![](create-plugin_output.png)
-
-This will create a new Backstage Plugin based on the ID that was provided. It will be built and
-added to the Backstage App automatically.
-
-*If `yarn start` is already running you should be able to see the default page for your new
-plugin directly by navigating to `http://localhost:3000/my-plugin`.*
-
-![](my-plugin_screenshot.png) -->
-
 ## Developing guidelines
 
 - Consider writing plugins in `TypeScript`.
 - Plan the directory structure of your plugin so that it becomes easy to manage.
-- Prefer using the Backstage components, otherwise go with
-  [Material-UI](https://material-ui.com/).
+- Prefer using the [Backstage components](https://backstage.io/storybook),
+  otherwise go with [Material-UI](https://material-ui.com/).
 - Check out the shared Backstage APIs before building a new one.
 
 ## Plugin concepts / API