Add references to VGG and Resnet variants

[ekagra-ranjan]

Adds missing paper references to vgg and resnet variants.

[fmassa]

LGTM, thanks!

Just waiting for CI to finish, and then this is good to merge!

[codecov-io]

Codecov Report

Merging #1088 into master will decrease coverage by 0.12%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1088      +/-   ##
==========================================
- Coverage   64.66%   64.53%   -0.13%     
==========================================
  Files          68       68              
  Lines        5406     5406              
  Branches      829      829              
==========================================
- Hits         3496     3489       -7     
- Misses       1661     1665       +4     
- Partials      249      252       +3

Impacted Files	Coverage Δ
torchvision/models/resnet.py	88.27% <ø> (ø)	⬆️
torchvision/models/vgg.py	89.55% <ø> (ø)	⬆️
torchvision/transforms/transforms.py	80.59% <0%> (-1.19%)	⬇️
torchvision/transforms/functional.py	71.09% <0%> (-0.29%)	⬇️

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