Add rationale for allow_tables_to_appear_in_same_query_config to chan…

…gelog because it's not obvious

CHANGELOG.md

@@ -26,7 +26,7 @@ in a way that makes the pools suitable for use in parallel tests.
 * Added `Json` and `Jsonb` support for the SQLite backend.
 * Added a `#[diesel::declare_sql_function]` attribute macro to easily define support for 
   multiple sql functions at once via an `extern "SQL"` block
-* Support `[print_schema] allow_tables_to_appear_in_same_query_config = "fk_related_tables"` to generate separate `allow_tables_to_appear_in_same_query!` calls containing only tables that are related through foreign keys. Without this option, or with an explicit value of `"all_tables"`, a single call is generated that contains all tables.
+* Support `[print_schema] allow_tables_to_appear_in_same_query_config = "fk_related_tables"` to generate separate `allow_tables_to_appear_in_same_query!` calls containing only tables that are related through foreign keys. (Default: `"all_tables"`.) It is not possible to build queries using two tables that don't appear in the same `allow_tables_to_appear_in_same_query!` call, but that macro generates O(n²) rust code, so this option may be useful to reduce compilation time. ([#4333](https://github.com/diesel-rs/diesel/issues/4333))
 
 ### Fixed