fix xref link

docs/modules/tutorials/nav.adoc

@@ -1,16 +1,16 @@
 * Tutorials
-** xref:beginner.adoc[Beginner tutorials]
-*** xref:hello_simpleapplication.adoc[Hello SimpleApplication]
-*** xref:hello_node.adoc[Hello Node]
-*** xref:hello_asset.adoc[Hello Asset]
-*** xref:hello_main_event_loop.adoc[Hello Update Loop]
-*** xref:hello_input_system.adoc[Hello Input System]
-*** xref:hello_material.adoc[Hello Material]
-*** xref:hello_animation.adoc[Hello Animation]
-*** xref:hello_picking.adoc[Hello Picking]
-*** xref:hello_collision.adoc[Hello Collision]
-*** xref:hello_terrain.adoc[Hello Terrain]
-*** xref:hello_audio.adoc[Hello Audio]
-*** xref:hello_effects.adoc[Hello Effects]
-*** xref:hello_physics.adoc[Hello Physics]
-*** xref:hellovector.adoc[Hello Vector3f]
+** xref:beginner/beginner.adoc[Beginner tutorials]
+*** xref:beginner/hello_simpleapplication.adoc[Hello SimpleApplication]
+*** xref:beginner/hello_node.adoc[Hello Node]
+*** xref:beginner/hello_asset.adoc[Hello Asset]
+*** xref:beginner/hello_main_event_loop.adoc[Hello Update Loop]
+*** xref:beginner/hello_input_system.adoc[Hello Input System]
+*** xref:beginner/hello_material.adoc[Hello Material]
+*** xref:beginner/hello_animation.adoc[Hello Animation]
+*** xref:beginner/hello_picking.adoc[Hello Picking]
+*** xref:beginner/hello_collision.adoc[Hello Collision]
+*** xref:beginner/hello_terrain.adoc[Hello Terrain]
+*** xref:beginner/hello_audio.adoc[Hello Audio]
+*** xref:beginner/hello_effects.adoc[Hello Effects]
+*** xref:beginner/hello_physics.adoc[Hello Physics]
+*** xref:beginner/hellovector.adoc[Hello Vector3f]