Add documentation for MarkDirectoryAsMagentoContentRot class

Added a Javadoc comment explaining the purpose of the MarkDirectoryAsMagentoContentRot class. This provides clarity on its role in marking a selected directory as a Magento content root.

Author: VitaliyBoyko

src/main/java/com/magento/idea/magento2plugin/actions/content/root/MarkDirectoryAsMagentoContentRot.java

@@ -29,6 +29,10 @@
 public class MarkDirectoryAsMagentoContentRot extends MarkRootActionBase {
     private Project project;
 
+    /**
+     * This action is used to mark a selected directory as
+     * a Magento content root within the project structure.
+     */
     public MarkDirectoryAsMagentoContentRot() {
         super();
         final Presentation presentation = this.getTemplatePresentation();