add webmention/pingback links

Author: keithamus

_includes/main.html

@@ -6,6 +6,8 @@
     {%- capture pagetitle %}{% if title %}{{ title }} –{% endif %} Web Components Guide{% endcapture %}
     <title>{{ pagetitle }}</title>
     <link rel="pgpkey authn" href="/key.gpg" />
+    <link rel="webmention" href="https://webmention.io/webcomponents.guide/webmention" />
+    <link rel="pingback" href="https://webmention.io/webcomponents.guide/xmlrpc" />
     <link rel="apple-touch-icon" sizes="180x180" href="/images/apple-touch-icon.png" />
     <link rel="icon" type="image/png" sizes="32x32" href="/images/favicon-32x32.png" />
     <link rel="icon" type="image/png" sizes="16x16" href="/images/favicon-16x16.png" />