Add inline prompt section for Copilot agent to assist updating workflows

[garrytrinder]

Suggestion from @pelikhan

Request

Add a dedicated section to the README that provides an inline prompt designed for the GitHub Copilot agent. This prompt should explain how to update workflows in a repository to use this action.

Details

• The prompt should be concise and actionable, guiding the Copilot agent on how to detect and update workflow files to use this action.
• The prompt should be formatted so it can be easily copied or referenced by users wishing to automate their workflow updates with Copilot.
• The Copilot agent will read the repository README to extract this prompt.

Acceptance Criteria

• README includes a clearly marked section containing an inline prompt for Copilot agent usage.
• The prompt provides step-by-step instructions or a direct example for updating workflows to use this action.

[garrytrinder]

@pelikhan do you have an example that you can share?