Improve documentation of how to fiddle with SCSI drives on FreeBSD.

Per suggestions from Achilleas Mantzios and Greg Smith.

Author: robertmhaas

doc/src/sgml/wal.sgml

@@ -87,7 +87,9 @@
         On <productname>FreeBSD</>, IDE drives can be queried using
         <command>atacontrol</command> and write caching turned off using
         <literal>hw.ata.wc=0</> in <filename>/boot/loader.conf</>;
-        SCSI drives use <command>sdparm</command>.
+        SCSI drives can be queried using <command>camcontrol identify</command>,
+        and the write cache both queried and changed using
+        <command>sdparm</command> when available.
       </para>
     </listitem>