Create documentation on dependabot, auto-approve and auto-merge workflows

This plugin has a dependabot file, as well as an auto-approve and auto-merge workflow file.

Create detailed user instructions on how to create and configure these three files for other repositories in this organisation, by forking the repository to their own GitHub account, cloning the fork locally, creating a new branch, adding the required files, pushing the branch, and creating a new PR.

It should contain information for how to set up the dependabot file for repositories that have composer dependancies, npm dependancies, or a combination of both.

As far as possible, use only the configurations in the relevant files for this repository to create the examples in the documenation.