Attempt to get some documentation going.

bindings/python/tests/implementations/test_byte_level_bpe.py

@@ -9,6 +9,8 @@ class TestByteLevelBPE:
         tokenizer = ByteLevelBPETokenizer.from_file(roberta_files["vocab"], roberta_files["merges"])
         output = tokenizer.encode("The quick brown fox jumps over the lazy dog")
 
+        tokenizer.save("roberta.json")
+
         assert output.ids == [133, 2119, 6219, 23602, 13855, 81, 5, 22414, 2335]
         assert output.tokens == [
             "The",