add attempt_count to config docs, set value to 1 in inital task save

django_q/migrations/0013_task_attempt_count.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.0.7 on 2020-08-11 15:17
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('django_q', '0012_auto_20200702_1608'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='task',
+            name='attempt_count',
+            field=models.IntegerField(default=0),
+        ),
+    ]