prompts: add neutral multilingual image-edit examples

[Senzo13]

Context

New users need safe examples that show what JoyBoy can do without relying on private packs or sensitive content.

Relevant files:

• docs/PROMPTS.md
• docs/GETTING_STARTED.md
• README.md

Suggested approach

Add a short set of neutral prompts in English and French for common tasks: background change, lighting, clothing restyle, object cleanup, outpaint/expand, text-to-image, and video prompt basics.

Acceptance criteria

• Adds 8-12 examples total.
• Examples cover image edit and text-to-image workflows.
• Examples avoid explicit/private content and provider secrets.
• The README links to the prompt examples without becoming too long.