Clean det ref

[flauted]

Very small changes to make the detection reference easier to use - removed hard-coded paths and documented multi-gpu.

[codecov-io]

Codecov Report

Merging #1109 into master will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #1109      +/-   ##
=========================================
+ Coverage   64.85%   64.9%   +0.05%     
=========================================
  Files          68      68              
  Lines        5417    5417              
  Branches      834     834              
=========================================
+ Hits         3513    3516       +3     
+ Misses       1647    1645       -2     
+ Partials      257     256       -1

Impacted Files	Coverage Δ
torchvision/transforms/transforms.py	81.53% <0%> (+0.58%)	⬆️

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[flauted]

Related to #1073 and #958.

[fmassa]

Thanks!