Removed void intro page to the tutorial

Summary: The 'extending flipper' introduction page didn't contain anything meaty, so collapsed it into the tutorial introduction, cleaning up the top level navigation.

Reviewed By: passy

Differential Revision: D25531718

fbshipit-source-id: ca0f98186e889e13cb97be8818db3588738e5039

docs/extending/index.mdx

@@ -3,6 +3,6 @@ id: index
 title: Clients and Plugins
 ---
 
-Flipper was designed with extensibility in mind from the start, to enable engineers to quickly build quality, easy-to-use tools for their own needs and applications.
+import {Redirect} from '@docusaurus/router';
 
-In addition to building plugins for the existing platforms, you can also extend the capabilities of Flipper to other platforms by conforming to the `FlipperClient` API. After this, you can make use of the existing desktop plugins by writing client plugins that conform to the same API.
+<Redirect to="/docs/tutorial/intro" />

docs/tutorial/intro.mdx

@@ -6,6 +6,10 @@ import useBaseUrl from '@docusaurus/useBaseUrl';
 
 <img alt="Android App Tutorial" src={useBaseUrl("img/android-tutorial.png")} />
 
+
+Flipper was designed with extensibility in mind from the start to enable engineers to quickly build quality, easy-to-use tools for their own needs and applications.
+In addition to building plugins for the existing platforms, you can also extend the capabilities of Flipper to other platforms by conforming to the `FlipperClient` API. After this, you can make use of the existing desktop plugins by writing client plugins that conform to the same API.
+
 In this tutorial, we show you how how easy it is to build a Flipper plugin
 for Android and iOS that extracts data from your native application and
 displays it in the desktop app.

website/docusaurus.config.js

@@ -41,7 +41,7 @@ const siteConfig = {
           position: 'right',
         },
         {
-          to: 'docs/extending/index',
+          to: 'docs/tutorial/intro',
           label: 'Extending',
           position: 'right',
         },

website/sidebars.js

@@ -52,7 +52,6 @@ module.exports = {
     Advanced: ['custom-ports', 'stetho'],
   },
   extending: {
-    'Extending Flipper': ['extending/index'],
     Tutorial: [
       'tutorial/intro',
       'tutorial/ios',