Add example showing how to override default reconciliation configs

Users override defaults by adding executionControl configuration
to their .mvn/maven-build-cache-config.xml file, not by creating
resource files. Added concrete example for maven-compiler-plugin.

Author: cowwoc

src/site/markdown/how-to.md

@@ -171,11 +171,31 @@ The build cache extension automatically tracks certain critical plugin propertie
 This default behavior prevents common cache invalidation issues, particularly in multi-module JPMS (Java Platform Module System)
 projects where compiler version changes can cause compilation failures.
 
-**Important:** When you explicitly configure `executionControl` for a plugin, your explicit configuration completely overrides
-the defaults for that plugin. However, defaults still apply to other plugins that aren't explicitly configured.
+**Overriding Defaults:** When you explicitly configure `executionControl` for a plugin, your explicit configuration completely
+overrides the defaults for that plugin. For example, to track only the `release` property for maven-compiler-plugin instead
+of the default `source`, `target`, and `release`:
 
-**Extending Beyond Defaults:** You can define reconciliation configurations for plugins that don't have built-in defaults by
-adding them to your `executionControl` configuration as shown in the examples above.
+```xml
+<cache xmlns="http://maven.apache.org/BUILD-CACHE-CONFIG/1.2.0">
+    <configuration>
+        ...
+    </configuration>
+    <executionControl>
+        <reconcile>
+            <plugins>
+                <plugin artifactId="maven-compiler-plugin" goal="compile">
+                    <reconciles>
+                        <reconcile propertyName="release"/>
+                    </reconciles>
+                </plugin>
+            </plugins>
+        </reconcile>
+    </executionControl>
+</cache>
+```
+
+This configuration in your `.mvn/maven-build-cache-config.xml` file replaces the built-in defaults. You can also define
+reconciliation configurations for plugins that don't have built-in defaults using the same syntax.
 
 ### Parameter Validation and Categorization