Added 'Privacy and Security Considerations' section to CSS Bikeshed Module (#241)

* [css-module-bikeshed] Added 'Privacy and Security Considerations'
section

* Turned contents of 'Privacy and Security Considerations' section into
issue

Author: SebastianZ

css-module-bikeshed/Overview.bs

@@ -159,3 +159,7 @@ Internal display model: the 'foo' property {#the-foo-property}
 			DOMString baz = "qux";
 		};
 	</pre>
+
+<h2 class=no-num id=priv-sec>Privacy and Security Considerations</h2>
+
+Issue: Make some considerations about privacy and security.