Add comparison docs for yolov5 & yolort

[zhiqwang]

This is a follow-up PR of #293 .

https://zhiqwang.com/yolov5-rt-stack/notebooks/comparison-between-yolort-vs-yolov5.html

[codecov]

Codecov Report

Merging #300 (a218c4d) into main (2e64a3f) will not change coverage.
The diff coverage is 100.00%.

❗ Current head a218c4d differs from pull request most recent head c6fd9ff. Consider uploading reports for the commit c6fd9ff to get more accurate results

@@           Coverage Diff           @@
##             main     #300   +/-   ##
=======================================
  Coverage   94.92%   94.92%           
=======================================
  Files          11       11           
  Lines         729      729           
=======================================
  Hits          692      692           
  Misses         37       37           

Flag	Coverage Δ
unittests	94.92% <100.00%> (ø)

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

Impacted Files	Coverage Δ
test/test_utils.py	75.51% <100.00%> (ø)

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