Fixed #24432 -- Added docs for ManyToManyFields that reside in and refer to the same model.

    If you don't specify an explicit ``through`` model, there is still an

    implicit ``through`` model class you can use to directly access the table

    created to hold the association. It has three fields:

    created to hold the association. It has three fields to link the models.

    If the source and target models differ, the following fields are

    generated:

    * ``id``: the primary key of the relation.

    * ``<containing_model>_id``: the ``id`` of the model that declares the

    * ``<other_model>_id``: the ``id`` of the model that the

      ``ManyToManyField`` points to.

    If the ``ManyToManyField`` points from and to the same model, the following 

    fields are generated:

    * ``id``: the primary key of the relation.

    * ``from_<model>_id``: the ``id`` of the instance which points at the

      model (i.e. the source instance).

    * ``to_<model>_id``: the ``id`` of the instance to which the relationship

      points (i.e. the target model instance).

    This class can be used to query associated records for a given model

    instance like a normal model.