feat: Add date started at organisation

See #33

people/migrations/0020_person_organisation_started_date.py

@@ -0,0 +1,18 @@
+# Generated by Django 2.2.10 on 2020-06-24 12:52
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('people', '0019_remove_person_core_member'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='person',
+            name='organisation_started_date',
+            field=models.DateField(null=True, verbose_name='Date started at this organisation'),
+        ),
+    ]