Added a new DistilGPT2 fine-tuning and generation Tutorial
Author: tripathiaakash
Pull request: yes

https://github.com/huggingface/transformers/pull/3177

# What does this PR do?

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Fixes # (issue)


## Before submitting
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 albert, bert, XLM: @LysandreJik
 GPT2: @LysandreJik, @patrickvonplaten
 tokenizers: @mfuntowicz
 Trainer: @sgugger
 Benchmarks: @patrickvonplaten
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 examples/distillation: @VictorSanh
 nlp datasets: [different repo](https://github.com/huggingface/nlp)
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Comments:
The tutorial has issues due old code. Will make another pull request with new code.