Improve documentation metadata

docs/_layouts/default.html

@@ -12,6 +12,10 @@
     <meta http-equiv="X-UA-Compatible" content="IE=edge">
     <meta name="viewport" content="width=device-width, initial-scale=1">
     <meta name="description" content="{{ site.data.project.description }}">
+    <meta property="og:site_name" content="HTTP Structured Fields for PHP">
+    <meta property="og:type" content="article">
+    <meta property="og:image" content="{{ site.baseurl }}/assets/img/httpsf-logo.png">
+    <meta property="og:description" content="{{ site.data.project.description }}">
     <link rel="icon" href="{{ site.baseurl }}/assets/img/httpsf-logo.svg" type="image/svg+xml">
     <title>{{ page.title }} - {{ site.data.project.title }}</title>
     <link rel="apple-touch-icon-precomposed" href="//theme.thephpleague.com/img/apple-touch-icon-precomposed.png">

docs/_layouts/homepage.html

@@ -4,6 +4,11 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <meta name="description" content="{{ site.data.project.description }}">
+    <meta property="og:title" content="{ site.data.project.tagline }} - {{ site.data.project.title }}">
+    <meta property="og:site_name" content="HTTP Structured Fields for PHP">
+    <meta property="og:type" content="article">
+    <meta property="og:image" content="{{ site.baseurl }}/assets/img/httpsf-logo.png">
+    <meta property="og:description" content="{{ site.data.project.description }}">
     <link rel="icon" href="{{ site.baseurl }}/assets/img/httpsf-logo.svg" type="image/svg+xml">
     <title>{{ site.data.project.tagline }} - {{ site.data.project.title }}</title>
     <link rel="preconnect" href="https://fonts.googleapis.com">