add ZBNF app to showcase

Summary:Thanks for submitting a pull request! Please provide enough information so that others can review your pull request:

(You can skip this if you're fixing a typo or adding an app to the Showcase.)

Explain the **motivation** for making this change. What existing problem does the pull request solve?

Prefer **small pull requests**. These are much easier to review and more likely to get merged. Make sure the PR does only one thing, otherwise please split it.

**Test plan (required)**

Demonstrate the code is solid. Example: The exact commands you ran and their output, screenshots / videos if the pull request changes UI.

Make sure tests pass on both Travis and Circle CI.

**Code formatting**

Look around. Match the style of the rest of the codebase. See also the simple [style guide](https://github.com/facebook/react-native/blob/master/CONTRIBUTING.md#style-guide).
Closes facebook#6680

Differential Revision: D3102712

fb-gh-sync-id: 2872886bc34128dae3326c664d446ffc8c97df03
fbshipit-source-id: 2872886bc34128dae3326c664d446ffc8c97df03

Author: chandu0101

Diff for: website/src/react-native/showcase.js

@@ -686,6 +686,12 @@ var apps = [
     link: 'https://itunes.apple.com/us/app/yazboz-batak-esli-batak-okey/id1048620855?ls=1&mt=8',
     author: 'Melih Mucuk',
   },
+  {
+    name: 'ZBNF - Zero Budget Natural Farming',
+    icon: 'https://lh3.googleusercontent.com/gnEBtkUTy89wgbRlEmbETJN9qzHgAAkcvCknWhZbomDRexFAjkU8W-DQFtFygTGeLtA=w300-rw',
+    link: 'https://play.google.com/store/apps/details?id=com.zbnf',
+    author: 'Chandra Sekhar Kode',
+  },
   {
     name: '天才段子手',
     icon: 'http://pp.myapp.com/ma_icon/0/icon_12236104_1451810987/96',