Add title to note box.

Co-authored-by: Marcos Cáceres <marcos@marcosc.com>

index.html

@@ -822,7 +822,7 @@ <h3>
  fingerprinting/privacy sensitive information that the user might
  not be aware of.
  </p>
- <p class="note">
+ <p class="note" title="Don't add identifiers to start URLs">
  It is bad practice for a developer to use the [=start URL=]
  to include information that uniquely identifies a user, as it would
  represent a fingerprint that is not cleared when the user clears