[Docs] Fixed some more links (#1648)

docs/plugins/create-a-plugin.md

@@ -40,4 +40,4 @@ for it can be found inside the plugin's `dev/` directory.
 
 [Next Step - Structure of a plugin](structure-of-a-plugin.md)
 
-[Back to Getting Started](README.md)
+[Back to Getting Started](../README.md)

docs/plugins/index.md

@@ -8,7 +8,7 @@ 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)
+![plugin](my-plugin_screenshot.png)
 
 ## Creating a plugin
 

docs/plugins/plugin-development.md

@@ -0,0 +1,78 @@
+# Plugin Development in Backstage
+
+Backstage plugins provide features to a Backstage App.
+
+Each plugin is treated as a self-contained web app and can include almost any
+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/).
+- Check out the shared Backstage APIs before building a new one.
+
+## Plugin concepts / API
+
+### Routing
+
+Each plugin is responsible for registering its components to corresponding
+routes in the app.
+
+The app will call the `createPlugin` method on each plugin, passing in a
+`router` object with a set of methods on it.
+
+```jsx
+import { createPlugin, createRouteRef } from '@backstage/core';
+import ExampleComponent from './components/ExampleComponent';
+
+export const rootRouteRef = createRouteRef({
+  path: '/new-plugin',
+  title: 'New plugin',
+});
+
+export const plugin = createPlugin({
+  id: 'new-plugin',
+  register({ router }) {
+    router.addRoute(rootRouteRef, ExampleComponent);
+  },
+});
+```
+
+#### `router` API
+
+```typescript
+addRoute(
+  target: RouteRef,
+  Component: ComponentType<any>,
+  options?: RouteOptions,
+): void;
+
+/**
+ * @deprecated See the `addRoute` method
+ */
+registerRoute(
+  path: RoutePath,
+  Component: ComponentType<any>,
+  options?: RouteOptions,
+): void;
+```

docs/plugins/publishing.md

@@ -3,9 +3,9 @@
 ## NPM
 
 NPM packages are published through CI/CD in the
-[.github/workflows/master.yml](../.github/workflows/master.yml) workflow. Every
-commit that is merged to master will be checked for new versions of all public
-packages, and any new versions will automatically be published to NPM.
+[.github/workflows/master.yml](../../.github/workflows/master.yml) workflow.
+Every commit that is merged to master will be checked for new versions of all
+public packages, and any new versions will automatically be published to NPM.
 
 ### Creating a new release
 
@@ -35,4 +35,4 @@ $ git push origin -u new-release
 And then create a PR. Once the PR is approved and merged into master, the master
 build will publish new versions of all bumped packages.
 
-[Back to Docs](README.md)
+[Back to Docs](../README.md)

docs/plugins/structure-of-a-plugin.md

@@ -104,4 +104,4 @@ either the one you already have (like nginx/haproxy/etc) or the proxy-backend
 plugin that we provide for the backstage backend.
 [Read more](../../plugins/proxy-backend/README.md)
 
-[Back to Getting Started](README.md)
+[Back to Getting Started](../README.md)