[css-align-3][editorial] Split priv-sec section, per W3C rules.

Author: tabatkins

css-align-3/Overview.bs

@@ -2531,11 +2531,17 @@ Changes</h2>
 			(<a href="https://github.com/w3c/csswg-drafts/issues/766">Issue 766</a>)
 	</ul>
 
-<h2 id="privacy-security">
-Privacy and Security Considerations</h2>
+<h2 id="privacy">
+Privacy Considerations</h2>
 
 	As a simple layout spec,
-	this introduces no new privacy or security considerations.
+	this introduces no new privacy considerations.
+
+<h2 id="security">
+Security Considerations</h2>
+
+	As a simple layout spec,
+	this introduces no new security considerations.
 
 <h2 class=no-num id="acknowledgments">
 Acknowledgments</h2>