Django CMS placeholder

gistfile1.py

## in models.py 

class Season(models.Model):
    title = models.CharField(max_length=255)
    season = models.IntegerField(choices=SEASONS, blank=True, null=True)
    year = models.IntegerField(blank=True, null=True)
    description = HTMLField(blank=True, null=True)
    description_placeholder = PlaceholderField('base_content', related_name='season_description', blank=True, null=True)
    calendar_file = FilerFileField(blank=True, null=True)
    
## in admin.py

class SeasonAdmin(PlaceholderAdminMixin, admin.ModelAdmin):
    pass


admin.site.register(Season, SeasonAdmin)