Use triagram similarity for user search

bookwyrm/migrations/0053_auto_20201014_1700.py

@@ -0,0 +1,15 @@
+# Generated by Django 3.0.7 on 2020-10-14 17:00
+
+from django.contrib.postgres.operations import TrigramExtension
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('bookwyrm', '0052_auto_20201005_2145'),
+    ]
+
+    operations = [
+        TrigramExtension()
+    ]