Fix links

Author: mattbrailsford

15/umbraco-commerce/tutorials/build-a-store/overview.md

@@ -12,9 +12,9 @@ This tutorial assumes that you already have the relevant site structure and cont
 
 ## Next steps
 
-{% content-ref url="installation/" %} Installation {% endcontent-ref %}  
-{% content-ref url="create-store/" %} Creating a Store {% endcontent-ref %}  
-{% content-ref url="create-product/" %} Creating your first Product {% endcontent-ref %}  
-{% content-ref url="cart-management/add-to-cart/" %} Implementing a Shopping Cart {% endcontent-ref %}  
-{% content-ref url="checkout/" %} Implementing a Checkout Flow {% endcontent-ref %}  
-{% content-ref url="permissions/" %} Configuring Store Permissions {% endcontent-ref %}  
+{% content-ref url="installation.md" %} Installation {% endcontent-ref %}  
+{% content-ref url="create-store.md" %} Creating a Store {% endcontent-ref %}  
+{% content-ref url="create-product.md" %} Creating your first Product {% endcontent-ref %}  
+{% content-ref url="create-cart.md" %} Implementing a Shopping Cart {% endcontent-ref %}  
+{% content-ref url="checkout.md" %} Implementing a Checkout Flow {% endcontent-ref %}  
+{% content-ref url="permissions.md" %} Configuring Store Permissions {% endcontent-ref %}