Update multi_base.md

s/sturcture/structure/

Author: joebowbeer

site/content/en/guides/example/multi_base.md

@@ -119,7 +119,7 @@ resources:
 namePrefix: cluster-a-
 ```
 
-## `directory sturcture`
+## `directory structure`
 > ```bash
 > .
 > ├── kustomization.yaml