[Doc] Update model zoo for documents

[ckkelvinchan]

This PR updates the README of each model in MMEditing.

[codecov]

Codecov Report

Merging #400 (32f516e) into master (0cfc334) will decrease coverage by 0.23%.
The diff coverage is 85.39%.

❗ Current head 32f516e differs from pull request most recent head 1bb2b3a. Consider uploading reports for the commit 1bb2b3a to get more accurate results

@@            Coverage Diff             @@
##           master     #400      +/-   ##
==========================================
- Coverage   80.75%   80.52%   -0.24%     
==========================================
  Files         187      188       +1     
  Lines       10015    10021       +6     
  Branches     1468     1482      +14     
==========================================
- Hits         8088     8069      -19     
- Misses       1723     1735      +12     
- Partials      204      217      +13     

Flag	Coverage Δ
unittests	80.52% <85.39%> (-0.22%)	⬇️

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

Impacted Files	Coverage Δ
mmedit/models/restorers/dic.py	68.14% <79.16%> (+5.28%)	⬆️
mmedit/models/losses/feature_loss.py	92.50% <92.50%> (ø)
mmedit/models/losses/__init__.py	100.00% <100.00%> (ø)
mmedit/models/restorers/ttsr.py	62.50% <0.00%> (-3.91%)	⬇️
...ls/components/stylegan2/generator_discriminator.py	83.73% <0.00%> (-2.41%)	⬇️
...ackbones/encoder_decoders/pconv_encoder_decoder.py	43.47% <0.00%> (-2.36%)	⬇️
mmedit/models/base.py	82.75% <0.00%> (-2.09%)	⬇️
...ones/encoder_decoders/two_stage_encoder_decoder.py	53.84% <0.00%> (-1.16%)	⬇️
...dels/backbones/encoder_decoders/encoders/resnet.py	66.01% <0.00%> (-0.97%)	⬇️
...s/backbones/encoder_decoders/gl_encoder_decoder.py	81.48% <0.00%> (-0.67%)	⬇️
... and 26 more

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