[Enhance] Add ScanNet alignment BC-breaking to compatibility document

[Wuziyi616]

I imitate the compatibility document in MMDet and write a (very initial and very naive) version. Only includes the change on ScanNet dataset.

[Wuziyi616]

Maybe we should add more terms to it, e.g. the model weight conversion for VoteNet on ScanNet?

[codecov]

Codecov Report

Merging #470 (66e0c6d) into master (f5a5103) will not change coverage.
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[Wuziyi616]

One question: should we upload new pre-trained weights for models trained on newly processed ScanNet?