docs: Added SavedModel export instructions in doc

[fg-mindee]

As per #5, this PR adds instructions for SavedModel saving / loading.

[codecov]

Codecov Report

Merging #246 (30151f7) into main (828a770) will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #246      +/-   ##
==========================================
+ Coverage   97.46%   97.52%   +0.05%     
==========================================
  Files          44       44              
  Lines        1896     1896              
==========================================
+ Hits         1848     1849       +1     
+ Misses         48       47       -1     

Flag	Coverage Δ
unittests	97.52% <ø> (+0.05%)	⬆️

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Impacted Files	Coverage Δ
...tr/models/detection/differentiable_binarization.py	94.73% <0.00%> (+0.40%)	⬆️

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[charlesmindee]

Thanks for the PR!