Add missing FROM clause to query example

Author: lovasoa

examples/official-site/sqlpage/migrations/47_link.sql

@@ -22,7 +22,8 @@ In `index.sql`, you can use the `link` function to generate the URL of the produ
 select ''list'' as component;
 select
     name as title,
-    sqlpage.link(''product'', json_object(''product_name'', name)) as link;
+    sqlpage.link(''product'', json_object(''product_name'', name)) as link
+from products;
 ```
 
 Using `sqlpage.link` is better than manually constructing the URL with `CONCAT(''product?product_name='', name)`,
@@ -72,4 +73,4 @@ VALUES
         'fragment',
         'An optional fragment (hash) to append to the URL to link to a specific section of the target page.',
         'TEXT'
-    );
+    );