message: chore: add soical metatags to demo
diff: <title>ReDoc Interactive Demo</title>
  <meta name="description" content="ReDoc Interactive Demo. OpenAPI/Swagger-generated API Reference Documentation" />
  <meta name="viewport" content="width=device-width, initial-scale=1">
  +
  + <meta property="og:title" content="ReDoc Interactive Demo">
  + <meta property="og:description" content="ReDoc Interactive Demo. OpenAPI/Swagger-generated API Reference Documentation">
  + <meta property="og:image" content="https://user-images.githubusercontent.com/3975738/37729752-8a9ea38a-2d46-11e8-8438-42ed26bf1751.png">
  + <meta name="twitter:card" content="summary_large_image">
  +
  <style>
  body {
  margin: 0;
  