Add explanations to payment methods, remove 'SU Core' method as now obsolete

RIGS/migrations/0051_alter_payment_method.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.2.19 on 2023-07-09 21:23
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('RIGS', '0050_event_forum_url'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='payment',
+            name='method',
+            field=models.CharField(blank=True, choices=[('C', 'Cash'), ('I', 'Internal'), ('E', 'External'), ('T', 'TEC Adjustment')], default='', max_length=2),
+        ),
+    ]