Improve documentation of new parameter for source path exclusion

Author: ascopes

maven-plugin-plugin/src/main/java/org/apache/maven/plugin/plugin/DescriptorGeneratorMojo.java

@@ -141,6 +141,21 @@ public class DescriptorGeneratorMojo extends AbstractGeneratorMojo {
      * that use annotations or documentation in an uncontrollable format that may conflict with the parsing
      * rules we utilise.
      *
+     * <p>Note that this only accepts <strong>source roots</strong>. It will not accept
+     * specific paths within a source root (e.g. specific packages). In this context, a source root
+     * would be considered to be a directory holding a full Java package structure which can be
+     * passed directly to {@code javac} for compilation, or {@code javadoc} for documentation.
+     *
+     * <p>As an example, the following configuration will prevent this goal scanning any
+     * generated sources from annotation processors:
+     *
+     * <pre>{@code
+     *   <excludedScanDirectories>
+     *     <excludedScanDirectory>${project.build.directory}/generated-sources/annotations</excludedScanDirectory>
+     *     <excludedScanDirectory>${project.build.directory}/generated-test-sources/annotations</excludedScanDirectory>
+     *   </excludedScanDirectories>
+     * }</pre>
+     *
      * @since TBC
      */
     @Parameter