add docs for the feature added in #1053 (#1061)

Author: Leanndrosouza

docs/reference/config.md

@@ -15,6 +15,7 @@ packages:
     emit_interface: false
     emit_exact_table_names: false
     emit_empty_slices: false
+    emit_exported_queries: false
     emit_json_tags: true
     json_tags_case_style: "camel"
     output_db_file_name: "db.go"
@@ -43,6 +44,8 @@ Each package document has the following keys:
   - If true, struct names will mirror table names. Otherwise, sqlc attempts to singularize plural table names. Defaults to `false`.
 - `emit_empty_slices`:
   - If true, slices returned by `:many` queries will be empty instead of `nil`. Defaults to `false`.
+- `emit_exported_queries`:
+  - If true, autogenerated SQL statement can be exported to be accessed by another package.
 - `emit_json_tags`:
   - If true, add JSON tags to generated structs. Defaults to `false`.
 - `json_tags_case_style`: