docs note about u_xyz data member on Custom Pivots

[skip ci]

docs/tinyorm/relationships.mdx

@@ -720,6 +720,18 @@ The same is true for the basic `Pivot` model, if you are using a basic pivot mod
 
 The reason for all of this is so that the `Model` knows how to generate a `std::variant` to hold the pivot model in the `Model::m_relations` data member hash map, which you get using the `Model::getRelationValue` or `Model::getRelation` methods.
 
+##### User Data Members on Custom Intermediate Table Models
+
+This is another nonstandard part of the custom pivot models. The `u_connection` and `u_timestamps` user data members and the `CREATED_AT` and `UPDATED_AT` static data members are ignored when obtaining pivot records from the database during the lazy or eager loading.
+
+Let's describe how these data members are resolved:
+
+ - `u_connection` - inferred from the parent model
+ - `u_timestamps` - true if obtained attributes contain both the `CREATED_AT` and `UPDATED_AT` attributes
+ - `CREATED_AT`, `UPDATED_AT` - inferred from the parent model, can be overridden using the `withTimestamps()` method
+
+All these data members are taken into account normally when you call the `create`, `save`, `update`, ... on the Custom Pivot models!
+
 ## Querying Relations
 
 Since all TinyORM relationships are defined via methods, you may call those methods to obtain an instance of the relationship without actually executing a query to load the related models. In addition, all types of TinyORM relationships also serve as [query builders](database/query-builder.mdx), allowing you to continue to chain constraints onto the relationship query before finally executing the SQL query against your database.