Add proper documentation for all versions on the module page & README.md

Problem/Motivation

Currently, the module page only contains information for the Drupal 7 release. We should add further installation / usage information on the module page for the 8.x-2.x release.

Proposed resolution

Add further installation / usage information on the module page for the 8.x-2.x release.

Also the other supported / recommended versions should be described and by their porpose, plan & differences.

Example for the module page:

Versions

• 3.x: Active development, Drupal 9/10 support, Drupal 8 support may end soon. Added field items wrapper & further functionality
• 8.x-2.x: Security fixes only, Drupal 8 support, no Drupal 10 support.
• 7.x-2.x: Active development, but maintenance fixes only. 7.x-1.x with further fixes. See comparison here.
• 7.x-1.x: Original Drupal 7 release, security fixes only.