Split up getting started docs

Summary:
This is a first step in breaking up the getting started docs.
Ultimately, the React Native Android and iOS bits will become
separate sections, too, but I won't to keep the diffs a bit smaller.
This one doesn't really do much apart from reorganising the current
content.

Reviewed By: mweststrate

Differential Revision: D20815235

fbshipit-source-id: 5c85b788211699a2a9f5808b9e2590c7db68a1c1

docs/getting-started/index.md

@@ -0,0 +1,19 @@
+---
+id: index
+title: Desktop App
+---
+
+Flipper helps you debug Android and iOS apps running in an emulator/simulator or connected physical development devices. Flipper consists of two parts:
+
+- The desktop app
+- The native mobile SDKs for Android and iOS
+
+To use Flipper, you need to add the mobile SDK to your app. If you are using React Native 0.62 or higher, this is largely done automatically for you.
+
+---
+
+The desktop part of Flipper doesn't need any particular setup. Simply download the latest build for [Mac](https://www.facebook.com/fbflipper/public/mac), [Linux](https://www.facebook.com/fbflipper/public/linux) or [Windows](https://www.facebook.com/fbflipper/public/windows) and launch it. In order to work properly, Flipper requires a working installation of the Android and (if where applicable) iOS development tools on your system, as well as the [OpenSSL](https://www.openssl.org) binary on your `$PATH`.
+
+Once you start Flipper and launch an emulator/simulator or connect a device, you will already be able to see the device logs in Flipper. To see app specific data, you need to integrate our native SDKs with your app.
+
+![Logs plugin](/docs/assets/initial.png)