Open Graph tags: use full url, add description

It seems like the absolute url (without domain) is making the image not
render in Twitter cards, and lack of a description is making some of the
embeds look strange. We'll add a default description for now and look to
override this soon.

tildes/tildes/__init__.py

@@ -47,6 +47,8 @@ def main(global_config: Dict[str, str], **settings: str) -> PrefixMiddleware:
     config.add_tween("tildes.http_method_tween_factory")
     config.add_tween("tildes.metrics_tween_factory")
 
+    config.add_static_view("images", "/images")
+
     config.add_request_method(is_safe_request_method, "is_safe_method", reify=True)
 
     # Add the request.redis request method to access a redis connection. This is done in

tildes/tildes/templates/base.jinja2

@@ -11,11 +11,12 @@
   <meta name="intercoolerjs:use-data-prefix" content="true">
   <meta name="csrftoken" content="{{ get_csrf_token() }}">
 
-  <meta property="og:image" content="/images/tildes-logo-144x144.png">
+  <meta property="og:image" content="{{ request.static_url("/images/tildes-logo-144x144.png") }}">
   <meta property="og:site_name" content="Tildes">
   <meta property="og:type" content="website">
   {% block meta_og_tags %}
   <meta property="og:title" content="{{ self.title() }}">
+  <meta property="og:description" content="Tildes: a non-profit community site">
   {% endblock %}
 
   {# Hardcoding each option isn't great, but I don't know a better method #}