Add canonical tag to readthedocs theme (#1669)

Close #1667

docs/about/release-notes.md

@@ -57,6 +57,7 @@ your global navigation uses more than one level, things will likely be broken.
 ### Other Changes and Additions to Version 1.1
 
 * Bugfix: Do not normalize URL fragments (#1655).
+* Add canonical tag to `readthedocs` theme (#1669).
 
 ## Version 1.0.4 (2018-09-07)
 

mkdocs/themes/readthedocs/base.html

@@ -8,6 +8,7 @@
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   {% if page and page.is_homepage %}<meta name="description" content="{{ config.site_description }}">{% endif %}
   {% if config.site_author %}<meta name="author" content="{{ config.site_author }}">{% endif %}
+  {% if page and page.canonical_url %}<link rel="canonical" href="{{ page.canonical_url }}">{% endif %}
   {% if config.site_favicon %}<link rel="shortcut icon" href="{{ config.site_favicon|url }}">
   {% else %}<link rel="shortcut icon" href="{{ 'img/favicon.ico'|url }}">{% endif %}
   {%- endblock %}