docs: add clarity and reference to JSON tags (#2819)

* docs: add clarity and reference to JSON tags

* Update docs/howto/structs.md

Added a link to the configuration reference on the JSON tags session.

* fix(docs): link to configuration reference

Author: kalogs-c

docs/howto/structs.md

@@ -31,7 +31,8 @@ CREATE TABLE authors (
 );
 ```
 
-sqlc can generate structs with JSON tags. The JSON name for a field matches
+sqlc can generate structs with JSON tags by adding the `emit_json_tags` key to the configuration file as it shows on [configuration reference](../reference/config.md).
+The JSON name for a field matches
 the column name in the database.
 
 ```go