[s2s] docs, document desired filenames nicely

[sshleifer]

No description provided.

[codecov]

Codecov Report

Merging #6525 into master will decrease coverage by 0.55%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #6525      +/-   ##
==========================================
- Coverage   80.59%   80.03%   -0.56%     
==========================================
  Files         156      156              
  Lines       28058    28058              
==========================================
- Hits        22612    22457     -155     
- Misses       5446     5601     +155     

Impacted Files	Coverage Δ
src/transformers/modeling_tf_openai.py	22.58% <0.00%> (-72.26%)	⬇️
src/transformers/tokenization_xlm_roberta.py	48.80% <0.00%> (-46.43%)	⬇️
src/transformers/tokenization_mbart.py	56.25% <0.00%> (-39.07%)	⬇️
src/transformers/tokenization_auto.py	95.55% <0.00%> (-2.23%)	⬇️
src/transformers/modeling_openai.py	80.96% <0.00%> (-1.30%)	⬇️
src/transformers/modeling_tf_utils.py	86.31% <0.00%> (-0.98%)	⬇️
src/transformers/configuration_utils.py	95.91% <0.00%> (-0.69%)	⬇️
src/transformers/generation_tf_utils.py	86.21% <0.00%> (-0.26%)	⬇️
src/transformers/pipelines.py	79.94% <0.00%> (+0.25%)	⬆️
src/transformers/file_utils.py	82.44% <0.00%> (+0.25%)	⬆️
... and 2 more

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