Fixed #15633 -- Improved docs for post_syncdb signal.

.. data:: django.db.models.signals.post_syncdb

   :module:

Sent by :djadmin:`syncdb` after it installs an application.

Sent by :djadmin:`syncdb` command after it installs an application, and

:djadmin:`flush` command.

Any handlers that listen to this signal need to be written in a particular

place: a ``management`` module in one of your :setting:`INSTALLED_APPS`. If

handlers are registered anywhere else they may not be loaded by

:djadmin:`syncdb`.

:djadmin:`syncdb`. It is important that handlers of this signal perform

idempotent changes (e.g. no database alterations) as this may cause the

:djadmin:`flush` management command to fail if it also ran during the

:djadmin:`syncdb` command.

Arguments sent with this signal: