welcome update to OpenMMLab 2.0

[vansin]

Looking forward to update to OpenMMLab 2.0

Hello, this issue is intended to guide on how to upgrade from OpenMMLab 1.0 to 2.0.

I'm Vansin, the technical operator of OpenMMLab. Last September, we announced the release of OpenMMLab 2.0 at the World Artificial Intelligence Conference. We invite you to upgrade your algorithm library to OpenMMLab 2.0, which can be used for both research and commercial purposes. If you have any questions, feel free to join us on the OpenMMLab Discord at https://discord.gg/amFNsyUBvm or add my WeChat: van-sin.

Here are the OpenMMLab 2.0 repos branches:

	OpenMMLab 1.0 branch	OpenMMLab 2.0 branch
MMEngine		0.x
MMCV	1.x	2.x
MMDetection	0.x 、1.x、2.x	3.x
MMAction2	0.x	1.x
MMClassification	0.x	1.x
MMSegmentation	0.x	1.x
MMDetection3D	0.x	1.x
MMEditing	0.x	1.x
MMPose	0.x	1.x
MMDeploy	0.x	1.x
MMTracking	0.x	1.x
MMOCR	0.x	1.x
MMRazor	0.x	1.x
MMSelfSup	0.x	1.x
MMRotate	1.x	1.x
MMYOLO		0.x