docs: add unique: false to belongs_to_many (#12481)

docs/manual/core-concepts/assocs.md

@@ -308,7 +308,7 @@ CREATE TABLE IF NOT EXISTS "ActorMovies" (
 
 
 Unlike One-To-One and One-To-Many relationships, the defaults for both `ON UPDATE` and `ON DELETE` are `CASCADE` for Many-To-Many relationships.
 Unlike One-To-One and One-To-Many relationships, the defaults for both `ON UPDATE` and `ON DELETE` are `CASCADE` for Many-To-Many relationships.
 
 
-Belongs-To-Many creates a unique key when primary key is not present on through model. This unique key name can be overridden using **uniqueKey** option.
+Belongs-To-Many creates a unique key on through model. This unique key name can be overridden using **uniqueKey** option. To prevent creating this unique key, use the ***unique: false*** option.
 
 
 ```js
 ```js
 Project.belongsToMany(User, { through: UserProjects, uniqueKey: 'my_custom_unique' })
 Project.belongsToMany(User, { through: UserProjects, uniqueKey: 'my_custom_unique' })