Add first examples of Actions example library (#21282)

Co-authored-by: Lucas Costi <lucascosti@users.noreply.github.com>

data/reusables/actions/note-understanding-example.md

@@ -0,0 +1,5 @@
+{% note %}
+
+**Note**: Each line of this workflow is explained in the next section at "[Understanding the example](#understanding-the-example)."
+
+{% endnote %}