Add a README for dc_ajax_add_cart_views sub-module

Problem/Motivation

The sub-module dc_ajax_add_cart_views is missing a README. Add a README for better documentation.

Proposed resolution

Probably instructions from the main README can be used. The instructions:

Installation and usage:

• If you want the ability to remove product from cart ajax-ifically, enable
  dc_ajax_add_cart_views module. This is provided as a sub-module.
• Edit the cart view, add field Remove button (Ajax).

should be used.

Remaining tasks

N/A

User interface changes

N/A

API changes

N/A

Data model changes

N/A