Add missing information on token_type_ids for roberta model (#19766)

* Add missing information on token_type_ids for roberta model

* Fix code format issues

* Fix code format issues

* Add more explicit document for token_type_ids for roberta

* Fix flake8 issues

* Fix flake8 issues

* Fix flake8 issues

* Fix flake8 issues

* Fix flake8 issues

src/transformers/models/roberta/modeling_roberta.py

@@ -649,11 +649,12 @@ ROBERTA_INPUTS_DOCSTRING = r"""
 
             [What are attention masks?](../glossary#attention-mask)
         token_type_ids (`torch.LongTensor` of shape `({0})`, *optional*):
-            Segment token indices to indicate first and second portions of the inputs. Indices are selected in `[0,
-            1]`:
+            Segment token indices to indicate first and second portions of the inputs. Indices are selected in `[0,1]`:
 
             - 0 corresponds to a *sentence A* token,
             - 1 corresponds to a *sentence B* token.
+            This parameter can only be used when the model is initialized with `type_vocab_size` parameter with value
+            >= 2. All the value in this tensor should be always < type_vocab_size.
 
             [What are token type IDs?](../glossary#token-type-ids)
         position_ids (`torch.LongTensor` of shape `({0})`, *optional*):