add security/privacy section

Author: astearns

css-shapes-1/Overview.bs

@@ -1166,3 +1166,10 @@ Since <a href="https://www.w3.org/TR/2011/WD-css3-exclusions-20111213/">December
 		<li>Clarified interaction with floats.</li>
 		<li>Clarified that an exclusion element establishes a new block formatting context.</li>
 	</ul>
+
+Privacy and Security Considerations {#priv-sec}
+===============================================
+
+	Since the <<image>> value of 'shape-outside' 
+	can expose some image data in a new way, 
+	use is limited to images with CORS approval.