Add metatags to show preview content when sharing website links

[goanpeca]

Some example data from https://2019.scipyla.org/ponentes/travis-oliphant/

<link rel="canonical" href="https://conf.scipyla.org/ponentes/travis-oliphant/" />
<meta property="og:locale" content="" />
<meta property="og:type" content="website" />
<meta property="og:title" content="" />
<meta property="og:description" content="" />
<meta property="og:url" content="http://conf.scipyla.org/ponentes/travis-oliphant/" />
<meta property="og:site_name" content="SciPy Latam 2019" />
<meta property="og:updated_time" content="2019-08-13T17:51:00+00:00" />
<meta property="og:image" content="http://conf.scipyla.org/ponentes/travis-oliphant/og-travis-oliphant.jpg" />
<meta property="og:image:secure_url" content="http://conf.scipyla.org/ponentes/travis-oliphant/og-travis-oliphant.jpg" />
<meta property="og:image:width" content="1067" />
<meta property="og:image:height" content="637" />

Which renders on slack and similar as: