Revert "Remove ludwig support"

 required by mailchimp: `composer require drupal/mailchimp`

 * In case you have manually downloaded this module, then you will need to

 install the [thinkshout/mailchimp-api-php](https://github.com/thinkshout/mailchimp-api-php) library manually as well. Use composer:

 `composer require thinkshout/mailchimp-api-php`

 install the thinkshout/mailchimp-api-php library manually as well:

   * Use composer: `composer require thinkshout/mailchimp-api-php`

   * Or if you cannot use composer, another option is to install it using the

   Ludwig module.

### Manual install using the Ludwig module

Composer is the recommended way to install and maintain a site. Site

administrators using Ludwig need to be careful when combining modules that

depend on external libraries, since there are no safeguards against incompatible

library versions or overlapping requirements.

Steps:

  1. Download and install the Ludwig module.

     https://www.drupal.org/project/ludwig

  2. Download and install the Mailchimp module.

  3. Ludwig generates a listing of libraries required by those modules. The

     Packages page at admin/reports/packages provides a download link for each

     missing library along with the paths where they should be placed.

CONFIGURATION

{

  "require": {

    "thinkshout/mailchimp-api-php": {

      "version": "v2.0.0",

      "url": "https://github.com/thinkshout/mailchimp-api-php/archive/v2.0.0.zip"

    }

  }

}