add example for ctrl text generation in docs

src/transformers/modeling_utils.py

@@ -624,6 +624,14 @@ class PreTrainedModel(nn.Module):
             input_ids = torch.tensor(tokenizer.encode(input_context)).unsqueeze(0)  # encode input context
             outputs = model.generate(input_ids=input_ids, max_length=40, do_sample=True, temperature=0.7, bos_token_id=tokenizer.bos_token_id, eos_token_ids=tokenizer.eos_token_id, num_beams=3)  # generate sequences using beam search decoding (3 beams)
             print('Generated: {}'.format(tokenizer.decode(outputs[0], skip_special_tokens=True)))
+
+            tokenizer = AutoTokenizer.from_pretrained('ctrl')   # Initialize tokenizer
+            model = AutoModelWithLMHead.from_pretrained('ctrl')    # Download model and configuration from S3 and cache.
+            input_context = 'Legal My neighbor is'  # "Legal" is one of the control codes for ctrl
+            input_ids = torch.tensor(tokenizer.encode(input_context)).unsqueeze(0)  # encode input context
+            outputs = model.generate(input_ids=input_ids, max_length=50, temperature=0.7, repetition_penalty=1.2)  # generate sequences using using greedy search
+            print('Generated: {}'.format(tokenizer.decode(outputs[0], skip_special_tokens=True)))
+
         """
 
         # We cannot generate if the model does not have a LM head