Noted that UnusedPrivateMethod may require configuring the classpath.

docs/config_usage.html

@@ -287,6 +287,15 @@
     <property name="ignoreFormat" value="Temp$"/>
 </module>
       </pre>
+
+      <h4>Notes</h4>
+
+      <ul class="body">
+        <li>The classpath may need to be configured to locate parameter type information. The
+        classpath configuration is dependent on the mechanism used to invoke Checkstyle.
+        </li>
+      </ul>
+
       <h4>Package</h4>
       <p class="body">
       com.puppycrawl.tools.checkstyle.checks.usage