Add more explanatory text under chart to tag stats pages (#8659)

Co-authored-by: Piyush Swain <piyush.swain@elitmus.com>

app/views/tag/_graph.html.erb

@@ -1,5 +1,5 @@
 <div id="chart"> </div>
-<i> The graphs above are stacked, and questions are counted both on their own as well as part of the tally for notes (because they are a form of note). </i>
+<i> The graphs above are stacked, and questions are counted both on their own as well as part of the tally for notes (because they are a form of note). Additional discrepancies may come from the tag page also listing questions tagged with "question:_____" but lacking the base tag, and also listing notes with only "child tags" of the base tag, in a system we are <a href="https://github.com/publiclab/plots2/issues/6367">planning to slowly deprecate</a>. </i>
     <br>
  <% if @tags.first.count.nil? %>
         <i> There are no posts for this tag yet </i>