docs: Updated docstrings of io, transforms & utils

[felixdittrich92]

#851

[codecov]

Codecov Report

Merging #859 (488294a) into main (096eb48) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #859      +/-   ##
==========================================
- Coverage   94.84%   94.82%   -0.02%     
==========================================
  Files         133      133              
  Lines        5200     5200              
==========================================
- Hits         4932     4931       -1     
- Misses        268      269       +1     

Flag	Coverage Δ
unittests	94.82% <ø> (-0.02%)	⬇️

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Impacted Files	Coverage Δ
doctr/io/html.py	100.00% <ø> (ø)
doctr/io/image/base.py	100.00% <ø> (ø)
doctr/io/pdf.py	93.33% <ø> (ø)
doctr/io/reader.py	100.00% <ø> (ø)
doctr/transforms/modules/base.py	94.59% <ø> (ø)
doctr/transforms/modules/pytorch.py	72.22% <ø> (ø)
doctr/transforms/modules/tensorflow.py	82.41% <ø> (ø)
doctr/utils/data.py	88.67% <ø> (ø)
doctr/utils/geometry.py	100.00% <ø> (ø)
doctr/utils/metrics.py	97.36% <ø> (ø)
... and 4 more

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[fg-mindee]

Thanks! Several comments in the review :)

[fg-mindee]

Thanks!