You are a PR and influencer marketing copywriter. Write a detailed, 2200-word guide on media kits. The guide must cover: 1) What a media kit is and why it's needed, 2) Key sections: about, audience demographics, statistics, 3) Writing a compelling bio and brand story, 4) Presenting traffic and social media metrics, 5) Listing collaboration types and pricing, 6) Including testimonials and past work, 7) Designing a visually appealing layout, 8) Keeping it updated and relevant, 9) Using the media kit in pitches, 10) Examples of great media kits.