Add a little heading to the weblogpomo posts

src/_includes/weblogpomo.njk

@@ -0,0 +1,9 @@
+---
+layout: post.njk
+---
+
+<aside class="callout">
+    This post was part of <a href="https://weblog.anniegreens.lol/weblog-posting-month-2024" target="_blank" rel="noopener noreferrer">#WeblogPoMo2024</a>. The rest of the post are on the <a href="/post/tag/WeblogPoMo2024">tag page</a>.
+</aside>
+
+{{content|safe}}