Add meta tags so our site previews well on social media

[elimisteve]

Example of how accessnow.org does it:

<title>Home - Access Now</title>
<meta name="description" content="Access Now defends and extends the digital rights of users at risk around the world."/>
<link rel="canonical" href="https://www.accessnow.org/" />
<meta property="og:locale" content="en_US" />
<meta property="og:type" content="website" />
<meta property="og:title" content="Access Now" />
<meta property="og:description" content="Defending and extending the rights of users at risk around the world." />
<meta property="og:url" content="https://www.accessnow.org/" />
<meta property="og:site_name" content="Access Now" />
<meta property="og:image" content="https://www.accessnow.org/cms/assets/uploads/2015/07/home-bg-banner.jpg" />
<meta property="og:image:secure_url" content="https://www.accessnow.org/cms/assets/uploads/2015/07/home-bg-banner.jpg" />
<meta name="twitter:card" content="summary" />
<meta name="twitter:description" content="Access Now defends and extends the digital rights of users at risk around the world." />
<meta name="twitter:title" content="Home - Access Now" />
<meta name="twitter:image" content="https://www.accessnow.org/cms/assets/uploads/2015/07/home-bg-banner.jpg" />