Issue #3209468 by joaopauloc.dev, pooja saraah, joachim: DrupalKernelInterface methods & DrupalKernel::sitePath should document the format of a site path

(cherry picked from commit 1fe7829e37)

core/lib/Drupal/Core/DrupalKernel.php

@@ -225,7 +225,12 @@ class DrupalKernel implements DrupalKernelInterface, TerminableInterface {
   protected static $isEnvironmentInitialized = FALSE;
 
   /**
-   * The site directory.
+   * The site path directory.
+   *
+   * Site path is relative to the app root directory.
+   * Usually defined as "sites/default".
+   *
+   * By default, drupal uses sites/default.
    *
    * @var string
    */

core/lib/Drupal/Core/DrupalKernelInterface.php

@@ -74,7 +74,9 @@ interface DrupalKernelInterface extends HttpKernelInterface, ContainerAwareInter
   public function getCachedContainerDefinition();
 
   /**
-   * Set the current site path.
+   * Set the current site path directory.
+   *
+   * Format: "folder-name/child-folder" usually uses "sites/default".
    *
    * @param string $path
    *   The current site path.
@@ -85,10 +87,10 @@ interface DrupalKernelInterface extends HttpKernelInterface, ContainerAwareInter
   public function setSitePath($path);
 
   /**
-   * Get the site path.
+   * Gets the site path directory.
    *
    * @return string
-   *   The current site path.
+   *   The current site path directory.
    */
   public function getSitePath();