Update export_model.md

[jin-s13]

Fix typos.

[CLAassistant]

All committers have signed the CLA.

[innerlee]

Need to add a line in changelog also

[codecov]

Codecov Report

Merging #399 (3e740f7) into master (ffa678c) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #399      +/-   ##
==========================================
- Coverage   86.59%   86.56%   -0.03%     
==========================================
  Files          98       98              
  Lines        6901     6901              
  Branches     1113     1113              
==========================================
- Hits         5976     5974       -2     
- Misses        708      709       +1     
- Partials      217      218       +1     

Flag	Coverage Δ
unittests	86.55% <ø> (-0.03%)	⬇️

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

Impacted Files	Coverage Δ
mmaction/datasets/pipelines/augmentations.py	94.72% <0.00%> (-0.28%)	⬇️

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