examples/seq2seq supports translation (#5202)

examples/seq2seq/train_distilbart_cnn.sh

@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+export PYTHONPATH="../":"${PYTHONPATH}"
+
+export BS=32
+export GAS=1
+
+python finetune.py \
+    --learning_rate=3e-5 \
+    --fp16 \
+    --gpus 1 \
+    --do_train \
+    --do_predict \
+    --val_check_interval 0.25 \
+    --n_val 500 \
+    --num_train_epochs 2 \
+    --freeze_encoder --freeze_embeds --data_dir $CNN_DIR \
+    --max_target_length 142 --val_max_target_length=142 \
+    --train_batch_size=$BS --eval_batch_size=$BS --gradient_accumulation_steps=$GAS \
+    --data_dir $CNN_DIR \
+    --model_name_or_path sshleifer/student_cnn_12_6 \
+    --tokenizer_name facebook/bart-large \
+    --output_dir distilbart-cnn-12-6 \
+    $@
+