diff --git a/layouts/shortcodes/heatmap.html b/layouts/shortcodes/heatmap.html
index bc41255b..c3e6bd2b 100644
--- a/layouts/shortcodes/heatmap.html
+++ b/layouts/shortcodes/heatmap.html
@@ -1,3 +1,4 @@
+<!-- credit to https://blog.douchi.space/hugo-blog-heatmap/ -->
 <div>
   <div style="display: flex; justify-content: center; align-items: center">
     <p style="margin-right: 15px; margin-bottom: 0; color: #333; padding: 8px">