fix: update landing page and enhance content XML structure

Updated the landing page reference in blueprint.json to point to the correct post ID. Enhanced content.xml by adding detailed export instructions, updating the generator version, and including a sample post and page structure for better clarity and usability.

Author: evrpress

.wordpress-org/blueprints/blueprint.json

@@ -1,6 +1,6 @@
 {
 	"$schema": "https://playground.wordpress.net/blueprint-schema.json",
-	"landingPage": "/wp-admin/post.php?post=4&action=edit",
+	"landingPage": "/wp-admin/post.php?post=428&action=edit",
 	"preferredVersions": {
 		"php": "8.3",
 		"wp": "latest"