Email should *not* be unique

turns out this is jank-city when you try to federate

bookwyrm/migrations/0052_auto_20201005_2145.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.0.7 on 2020-10-05 21:45
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('bookwyrm', '0051_auto_20201005_2142'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='user',
+            name='email',
+            field=models.EmailField(blank=True, max_length=254, verbose_name='email address'),
+        ),
+    ]