add og description tag

templates/main.html

@@ -11,6 +11,7 @@
     <meta name="viewport" content="width=device-width, initial-scale=1">
     <meta property="og:site_name" content="{{garden_title}}" />
     <meta property="og:title" content="{{page_title}}" />
+    <meta property="og:description" content="{{content | striptags | truncate(length=256)}}" />
     <meta property="og:type" content="article" />
     <meta property="og:url" content="https://{{server_name}}/{{path}}" />
     <meta property="og:image" content="/static/favicon.png" />