Metadata for social media previews / unfurling isn't included

[bmann]

Just pasting a link to memex into our Discord, and no image preview or description.

There's some siteMetadata in gatsby-config.js, but it's not in the published version of the website: https://github.com/WorldBrain/Website/blob/9d47a9869d7562a98a4291aa5ed1083287acb754/gatsby-config.js

Which looks to just pull from html.tsx right now.

Here's an example template (a lightly scrubbed version of what I just added to some Fission apps):

<!-- Favicons & Mobile settings -->
<link rel="apple-touch-icon" sizes="180x180" href="apple-touch-icon.png" />
<link rel="icon" type="image/png" sizes="32x32" href="favicon-32x32.png" />
<link rel="icon" type="image/png" sizes="16x16" href="favicon-16x16.png" />
<link rel="manifest" href="site.webmanifest" />
<link rel="mask-icon" href="safari-pinned-tab.svg" color="#6446fa" />
<meta name="msapplication-TileColor" content="#1e2347" />
<meta name="theme-color" content="#1e2347" />
<!-- Social Metadata -->
<!-- Primary Meta Tags -->
<meta name="title" content="PAGE TITLE">
<meta name="description" content="DESCRIPTION">
<!-- Open Graph / Facebook -->
<meta property="og:type" content="website">
<meta property="og:url" content="https://getmemex.com/">
<meta property="og:title" content="PAGE TITLE">
<meta property="og:description" content="DESCRIPTION">
<meta property="og:image" content="FULL PATH TO IMAGE - Facebook Size">
<!-- Twitter -->
<meta property="twitter:card" content="summary_large_image">
<meta name="twitter:site" content="@WorldBrain">
<meta property="twitter:url" content="https://getmemex.com">
<meta property="twitter:title" content="PAGE TITLE">
<meta property="twitter:description" content="DESCRIPTION">
<meta property="twitter:image" content="FULL PATH TO IMAGE - Twitter Size">
<meta name="twitter:label1" value="Subscribe today for end-to-end encrypted sync with mobile" />
<meta name="twitter:data1" value="Just 2€ per month or 20€ per year" />

Those Twitter data labels are read in by (among others) Slack when you paste in links there.