Fix getting-started link (#1005)

Summary:
Fixes https://github.com/facebook/flipper/issues/1003
Pull Request resolved: https://github.com/facebook/flipper/pull/1005

Test Plan: https://fbflipper.com/docs/getting-started/index.html works.

Reviewed By: jknoxville

Differential Revision: D20993208

Pulled By: passy

fbshipit-source-id: 1f0e3dd9a8d13f76018117dbc73dd1513a0df3c2

website/pages/docs/en/index.js

@@ -14,7 +14,7 @@ class Docs extends React.Component {
     return (
       <script
         dangerouslySetInnerHTML={{
-          __html: "window.location.href = '/docs/getting-started.html'",
+          __html: "window.location.href = '/docs/getting-started/index.html'",
         }}
       />
     );