Add examples, highlighting the benefits of using Preprocess

Problem/Motivation

There is an example in the README.md file on how to use the module, which is great.

Personally, as primarily a site builder and not so much a coder, it would be awesome with some examples on how you would have to do certain things now (add three files, put this code in here) and then an example on how to do the same thing with this module, in a single file, and with less code, to make the benefits of using it clearer.

It probably shouldn't be added in the README.md file, but rather a dedicated documentation Guide, under https://www.drupal.org/docs/extending-drupal/contributed-modules/contrib... → .

Steps to reproduce

Proposed resolution

• Add documentation guide and pages under https://www.drupal.org/docs/extending-drupal/contributed-modules/contrib... →
• Add example of the current steps required to preprocess, and the improved process with this module

Remaining tasks

User interface changes

API changes

Data model changes