pipelimit Document dependency on the sl module

Closes issue #69

modules/pipelimit/README

@@ -150,6 +150,7 @@ Chapter 1. Admin Guide
 
    The following modules must be loaded before this module:
      * database connection module.
+     * sl: Stateless Request Handling.
 
 2.2. External Libraries or Applications
 

modules/pipelimit/doc/pipelimit_admin.xml

@@ -45,6 +45,11 @@
 				<emphasis>database connection module</emphasis>.
 			</para>
 			</listitem>
+			<listitem>
+			<para>
+				<emphasis>sl: Stateless Request Handling</emphasis>.
+			</para>
+			</listitem>
 			</itemizedlist>
 		</para>
 	</section>