Update similarity_model.py

Update verbose printing to display the count of indexed items.

Verbose output was missing an f-string prefix and also returned the entire shape. Now we just return the number of examples.

tensorflow_similarity/models/similarity_model.py

@@ -360,7 +360,7 @@ def index(
         """
 
         if verbose:
-            print("[Indexing {tf.shape(x)} points]")
+            print(f"[Indexing {tf.shape(x)[0]} points]")
             print("|-Computing embeddings")
         with tf.device("/cpu:0"):
             x = tf.convert_to_tensor(np.array(x))