about FatraGNN, including model,datasets and example

[taorann]

Description

Checklist

Please feel free to remove inapplicable items for your PR.

• The PR title starts with [$CATEGORY] (such as [NN], [Model], [Doc], [Feature]])
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage
• Code is well-documented
• To the best of my knowledge, examples are either not affected by this change,
  or have been fixed to be compatible with this change
• Related issue is referred in this PR

Changes

[xy-Ji]

Model file was not well-documented and comments should be in English.
Please add a readme document to the examples/fatragnn folder.

[gyzhou2000]

提交对应数据集和模型的pytest文件，数据集pytest内容可参考 GammaGL/tests/datasets/test_acm.py 的内容