Add a note about NaN on the stddev column

example/fetch_benchmark.html

diff --git a/example/fetch_benchmark.html b/example/fetch_benchmark.html
index 788d14d..dbaf225 100644
--- a/example/fetch_benchmark.html
+++ b/example/fetch_benchmark.html
@@ -159,7 +159,13 @@
       id="summary" rows="20" style="width: 100%" readonly></textarea>
 </div>
 
-Note: Effect of RTT and time spent for ArrayBuffer creation in receive benchmarks are not eliminated.
+<div id="note_div">
+  Note:
+  <ul>
+    <li>Effect of RTT and time spent for ArrayBuffer creation in receive benchmarks are not eliminated.</li>
+    <li>The Stddev column shows NaN when the number of iterations is set to 1.</li>
+  </ul>
+</div>
 
 </body>
 </html>

example/xhr_benchmark.html

diff --git a/example/xhr_benchmark.html b/example/xhr_benchmark.html
index 4ff2ce0..8b296cc 100644
--- a/example/xhr_benchmark.html
+++ b/example/xhr_benchmark.html
@@ -208,7 +208,13 @@
       id="summary" rows="20" style="width: 100%" readonly></textarea>
 </div>
 
-Note: Effect of RTT and time spent for ArrayBuffer creation in receive benchmarks are not eliminated.
+<div id="note_div">
+  Note:
+  <ul>
+    <li>Effect of RTT and time spent for ArrayBuffer creation in receive benchmarks are not eliminated.</li>
+    <li>The Stddev column shows NaN when the number of iterations is set to 1.</li>
+  </ul>
+</div>
 
 </body>
 </html>