Use Jekyll SEO Tag to generate the search engine HEAD meta.

This commit moves the site to use the official Jekyll SEO Tag
plugin (https://github.com/jekyll/jekyll-seo-tag) to generate the
search-engine meta in the HEAD of each page. The title and canonical
URL output should be largely the same as before, but with additional
metadata, such as JSON-LD (for richer indexing), Twitter card
metadat, etc.

Like the other plugins, this should largely work out-of-the-box,
with no additional day-to-day configuration, but is customizable
where desired.

_config.yml

@@ -33,3 +33,9 @@ gems:
   - jekyll-redirect-from
   - jekyll-feed
   - jekyll-sitemap
+  - jekyll-seo-tag
+
+# SEO
+logo: /images/favicon.png
+twitter:
+  username: kubernetesio