Add UNIX keyword... didn't add a short version, don't think there is one.

docs/security.html

@@ -84,7 +84,8 @@ TUSED		$O	User's time online this call (minutes, 0-255)
 UDR		$K	User's upload/download ratio (0-100)
 UDFR		$D	User's upload/download file ratio (0-100)
 USER		$U	User's number (1-xxxx)
-WIP			User has WIP compatible terminal (no value argument)</pre>
+WIP			User has WIP compatible terminal (no value argument)
+UNIX			BBS is running on a UNIX clone</pre>
 <h2><a name="GeneralUsageExamples">[7.3] - ARS General Usage Examples</a></h2>
 <pre><b>General Example #1</b>