docs: Update preview icons (#16)

Signed-off-by: Artem Kladov <artem.kladov@flant.com>

Author: z9r5

layouts/_partials/head.html

@@ -10,11 +10,16 @@
 <meta name="title" content="{{ .Title }} | {{ .Site.Title }}">
 
 <!-- Open Graph / Facebook -->
-<meta property="og:type" content="website">
+<meta property="og:type" content="article">
 <meta property="og:url" content="{{ strings.TrimSuffix "readme.html" .Permalink  }}">
 <meta property="og:title" content="{{ .Title }} | {{ .Site.Title }}">
 <meta property="og:description" content="{{ $description }}">
-<meta property="og:image" content="{{ site.BaseURL }}/favicon-32x32.png" />
+{{ if .Site.Params.productCode }}
+<meta property="og:image" content="/images/og/{{ .Site.Params.productCode }}.png" />
+<meta property="og:image:width" content="1200">
+<meta property="og:image:height" content="628">
+<meta property="og:image:type" content="image/png">
+{{ end }}
 
 <!-- Twitter -->
 <meta name="twitter:card" content="summary">