Clarify that the saltLength parameter of RSA-PSS is in bytes, not bits (#400)

Author: panva

spec/Overview.html

@@ -4963,7 +4963,7 @@ <h4><dfn data-idl id="dfn-RsaPssParams">RsaPssParams</dfn> dictionary</h4>
   required [EnforceRange] unsigned long saltLength;
 };
           </pre>
-          <p>The <dfn data-idl data-dfn-for=RsaPssParams id="dfn-RsaPssParams-saltLength">saltLength</dfn> member represents the desired length of the random salt.</p>
+          <p>The <dfn data-idl data-dfn-for=RsaPssParams id="dfn-RsaPssParams-saltLength">saltLength</dfn> member represents the desired length of the random salt in bytes.</p>
         </section>
         <section id="rsa-pss-operations">
           <h4>Operations</h4>