New README.md file

I have created the new increased version of readme file:

CONTENTS OF THIS FILE
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 * Introduction
 * Recommended modules
 * Installation
 * Configuration
 * Troubleshooting
 * Maintainers

INTRODUCTION
------------
 
 * Nexus is a Drupal 8 theme. The theme is not dependent on any
   core theme. Its very light weight for fast loading with modern look.
   Simple and clean design
   Drupal standards compliant
   Implementation of a JS Slideshow
   Multi-level drop-down menus
   Footer with 4 regions
   A total of 10 regions

RECOMMENDED MODULES
-------------------

 * No extra module is required.

INSTALLATION
------------

 * Install as usual, see
   https://www.drupal.org/docs/user_guide/en/extend-theme-install.html

CONFIGURATION
-------------

 * Configuration is aviable over Settings section in Apperance tab.

TROUBLESHOOTING
---------------

 * Theme is compatible and tested on IE7, IE8, IE9+, Opera, Firefox, Chrome browsers, so it won't make any troubles.


MAINTAINERS
-----------

 * https://www.drupal.org/u/dipakmdhrm
   https://www.drupal.org/u/karmen
   https://www.drupal.org/u/nesta_
   https://www.drupal.org/u/devsaran

PORTED TO DRUPAL 8 BY
---------------------

 * https://www.drupal.org/u/dipakmdhrm
   http://www.dipakyadav.com

DONATIONS
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 * Paypal ID : donation@devsaran.com

Done for Google Code-In task.