Fix doc about split

bindings/python/src/pre_tokenizers.rs

@@ -324,8 +324,11 @@ impl PyWhitespaceSplit {
 ///
 /// Args:
 ///     pattern (:obj:`str` or :class:`~tokenizers.Regex`):
-///         A pattern used to split the string. Usually a string or a a regex built with `tokenizers.Regex`
-///
+///         A pattern used to split the string. Usually a string or a a regex built with `tokenizers.Regex`.
+///         If you want to use a regex pattern, it has to be wrapped around a `tokenizer.Regex`,
+///         otherwise we consider is as a string pattern. For example `pattern="1|2"`
+///         means you want to split on `1|2` (imagine a csv file for example), while
+///         `patter=tokenizer.Regex("1|2")` means you split on either '1' or '2'.
 ///     behavior (:class:`~tokenizers.SplitDelimiterBehavior`):
 ///         The behavior to use when splitting.
 ///         Choices: "removed", "isolated", "merged_with_previous", "merged_with_next",