fix(challenges): add note at bottom of description in d3 challenge

Add a short message in note at bottom of description in d3 challenge

ISSUES CLOSED: #17767

challenges/04-data-visualization/data-visualization-with-d3.json

@@ -1867,7 +1867,8 @@
         "A scatter plot is another type of visualization. It usually uses circles to map data points, which have two values each. These values tie to the <code>x</code> and <code>y</code> axes, and are used to position the circle in the visualization.",
         "SVG has a <code>circle</code> tag to create the circle shape. It works a lot like the <code>rect</code> elements you used for the bar chart.",
         "<hr>",
-        "Use the <code>data()</code>, <code>enter()</code>, and <code>append()</code> methods to bind <code>dataset</code> to new <code>circle</code> elements that are appended to the SVG canvas."
+        "Use the <code>data()</code>, <code>enter()</code>, and <code>append()</code> methods to bind <code>dataset</code> to new <code>circle</code> elements that are appended to the SVG canvas.",
+        "<strong>Note</strong><br>The circles won't be visible because we haven't set their attributes yet. We'll do that in the next challenge."
       ],
       "tests": [
         {