Issue #3364098: Replace README.txt with README.md and update README.md file

README.md

+CONTENTS
+--------
+
+Introduction
+Requirements
+Installation
+Configuration
+Maintainers
+
+
+INTRODUCTION
+------------
+Custom admin theme is a module for the frontend development of the 
+administration theme.
+
+In many occasions it is necessary to fix some styles found in the 
+administration themes
+and it is not convenient to use our "custom-theme", so it is necessary to use
+the module.
+
+Module project page:
+http://drupal.org/project/zcat
+
+To submit bug reports and feature suggestions, or to track changes:
+http://drupal.org/project/issues/zcat
+
+REQUIREMENTS
+------------
+None.
+
+INSTALLATION
+------------
+Install as you would normally install a contributed Drupal module. 
+Visit: https://www.drupal.org/docs/extending-drupal/installing-modules
+
+CONFIGURATION
+-------------
+The module allows access to change styles in the administration in two ways,
+through the included css or
+through a file placed in /theme/custom/[yourCustomTheme]/css/custom-admin.css.
+
+To let the module know the name of your theme you can indicate it in the
+configuration screen: 
+"/admin/config/custom-admin-theme, type the name of your theme and click
+on save."
+
+MAINTAINER
+-----------
+gserramar - https://www.drupal.org/user/3673360