Replace root README with exact badge-rich BasicMails template

[Copilot]

This PR replaces the repository-root README.md with the exact markdown requested in the issue, including the specified badge format and copy-ready project documentation. The goal is to provide a polished, consistent landing page aligned with the previously approved content.

• Scope

  • Replaced /README.md content in full to match the provided template exactly.
  • Preserved all required formatting details: badge URLs, heading structure, horizontal rules, code fences, and inline examples.

• README content updates

  • Added top-level badge block using <img> tags for release, license, language, stars, and issues.
  • Included structured sections: Why BasicMails, Features, Quick Start, Configuration, Development, Contributing, Security, License, Contact.
  • Included the exact Table of Contents format and example snippets as provided.

• Example included in README

  import { BasicMailsClient } from 'basicmails'
  
  const client = new BasicMailsClient({ apiKey: process.env.BASICMAILS_API_KEY })
  await client.send({
    to: 'friend@example.com',
    from: 'you@basicmails.local',
    subject: 'Hello from BasicMails',
    text: 'This is a quick test email.'
  })