Updated readme [skip ci]

Author: ankane

README.md

@@ -100,23 +100,23 @@ Also supports `Sum`
 Add an approximate index
 
 ```python
-from pgvector.django import IvfflatIndex, HnswIndex
+from pgvector.django import HnswIndex, IvfflatIndex
 
 class Item(models.Model):
     class Meta:
         indexes = [
-            IvfflatIndex(
+            HnswIndex(
                 name='my_index',
                 fields=['embedding'],
-                lists=100,
+                m=16,
+                ef_construction=64,
                 opclasses=['vector_l2_ops']
             ),
             # or
-            HnswIndex(
+            IvfflatIndex(
                 name='my_index',
                 fields=['embedding'],
-                m=16,
-                ef_construction=64,
+                lists=100,
                 opclasses=['vector_l2_ops']
             )
         ]
@@ -183,14 +183,14 @@ Add an approximate index
 
 ```python
 index = Index('my_index', Item.embedding,
-    postgresql_using='ivfflat',
-    postgresql_with={'lists': 100},
+    postgresql_using='hnsw',
+    postgresql_with={'m': 16, 'ef_construction': 64},
     postgresql_ops={'embedding': 'vector_l2_ops'}
 )
 # or
 index = Index('my_index', Item.embedding,
-    postgresql_using='hnsw',
-    postgresql_with={'m': 16, 'ef_construction': 64},
+    postgresql_using='ivfflat',
+    postgresql_with={'lists': 100},
     postgresql_ops={'embedding': 'vector_l2_ops'}
 )