Add transforms doc to more datasets

[TheCodez]

No description provided.

[codecov-io]

Codecov Report

Merging #1038 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1038   +/-   ##
=======================================
  Coverage   63.46%   63.46%           
=======================================
  Files          65       65           
  Lines        5154     5154           
  Branches      772      772           
=======================================
  Hits         3271     3271           
  Misses       1661     1661           
  Partials      222      222

Impacted Files	Coverage Δ
torchvision/datasets/coco.py	29.26% <ø> (ø)	⬆️
torchvision/datasets/voc.py	22.1% <ø> (ø)	⬆️
torchvision/datasets/sbd.py	31.25% <ø> (ø)	⬆️

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[fmassa]

Thanks!

[fmassa]

@TheCodez could you also send a follow-up PR mentioning that either transform / target_transform or transforms is applied to the data?