Update pie usage link (#5048)

Author: sy-records

install/pie.xml

@@ -29,7 +29,7 @@ pie install mongodb/mongodb-extension
    </programlisting>
   </example>
   <simpara>
-   The <link xlink:href="&url.pie;/blob/main/docs/usage.md">"PIE
+   The <link xlink:href="&url.pie.usage;">"PIE
    Usage" documentation</link> goes into this in more depth.
   </simpara>