[Feature] Add config and pre-trained model for flownet2 on FlyingChairs

[Zachary-66]

Motivation

Add config and pre-trained model for flownet2 on FlyingChairs.

Modification

1. Add configs/flownet2/flownet2_8x1_slong_flyingchairs_384x448.py
2. Fix configs/flownet2/metafile.yml
3. Fix configs/flownet2/REDAME.md
4. Fix configs/flownet2/flownet2css_8x1_sfine_flyingthings3d_subset_384x768.py

[codecov]

Codecov Report

Merging #163 (f9ad309) into master (8736fea) will decrease coverage by 0.19%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #163      +/-   ##
==========================================
- Coverage   68.88%   68.68%   -0.20%     
==========================================
  Files          92       92              
  Lines        5148     5148              
  Branches      733      733              
==========================================
- Hits         3546     3536      -10     
- Misses       1488     1498      +10     
  Partials      114      114              

Flag	Coverage Δ
unittests	68.68% <ø> (-0.20%)	⬇️

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

Impacted Files	Coverage Δ
mmflow/datasets/pipelines/transforms.py	78.16% <0.00%> (-1.67%)	⬇️

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