Use post url for finding utterances issue

blog/templates/macros.html

@@ -7,3 +7,12 @@
         </div>
     </article>
 {% endmacro post_link %}
+
+{% macro utterances() %}
+    <script src="https://utteranc.es/client.js"
+        repo="phil-opp/blog_os"
+        issue-term="url"
+        crossorigin="anonymous"
+        async>
+    </script>
+{% endmacro utterances %}