Add utterance.es support (#127)

A lightweight comments widget built on GitHub issues.

layouts/partials/blog_single.html

@@ -91,6 +91,19 @@
             </div>
             {{ end }}
 
+            <!-- utteranc -->
+            {{ if .Site.Params.utteranc.enable }}
+            <div class="post bg-white">
+                <script src="https://utteranc.es/client.js"
+                    repo= "{{ .Site.Params.utteranc.repo }}"
+                    issue-term="{{ .Site.Params.utteranc.issueTerm }}"
+                    theme="{{ default "github-light" .Site.Params.utteranc.theme }}"
+                    crossorigin="anonymous"
+                    async>
+                </script>
+            </div>
+            {{ end }}
+
             {{ if .Site.Params.issoHost }}
             <br>
             <div class="isso" id="isso-thread"></div>