[1.1.X] Fixed #13282 -- Clarified documentation around week_day filtering in...

For date/datetime fields, a 'day of the week' match.

Takes an integer value representing the day of week from 1 (Sunday) to 7

(Saturday).

Example::

    Entry.objects.filter(pub_date__week_day=2)

SQL equivalent::

    SELECT ... WHERE EXTRACT('dow' FROM pub_date) = '2';

(The exact SQL syntax varies for each database engine.)

(No equivalent SQL code fragment is included for this lookup because

implementation of the relevant query varies among different database engines.)

Note this will match any record with a pub_date that falls on a Monday (day 2

of the week), regardless of the month or year in which it occurs. Week days