Docstrings for from_fiftyone

[ethanwharris]

What does this PR do?

Part of #957

Fixes #1111

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• Did you write any new necessary tests? [not needed for typos/docs]
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[codecov]

Codecov Report

Merging #1136 (be7214f) into master (fd1a2e4) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1136      +/-   ##
==========================================
+ Coverage   89.03%   89.07%   +0.04%     
==========================================
  Files         285      285              
  Lines       12980    13002      +22     
==========================================
+ Hits        11557    11582      +25     
+ Misses       1423     1420       -3     

Flag	Coverage Δ
unittests	89.07% <100.00%> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
flash/core/utilities/imports.py	92.81% <100.00%> (+0.17%)	⬆️
flash/image/classification/data.py	97.63% <100.00%> (+0.05%)	⬆️
flash/image/classification/input.py	100.00% <100.00%> (+1.20%)	⬆️
flash/image/detection/data.py	100.00% <100.00%> (ø)
flash/image/detection/input.py	100.00% <100.00%> (+2.73%)	⬆️
flash/image/segmentation/data.py	100.00% <100.00%> (ø)
flash/image/segmentation/input.py	100.00% <100.00%> (ø)
flash/video/classification/data.py	100.00% <100.00%> (ø)
flash/video/classification/input.py	95.65% <100.00%> (+0.24%)	⬆️
... and 1 more

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