[Docs] Update citation

[wangruohui]

If cite from github :

@software{MMEditing_Contributors_MMEditing_OpenMMLab_Image_2022,
author = {{MMEditing Contributors}},
license = {Apache-2.0},
month = {3},
title = {{MMEditing: OpenMMLab Image and Video Editing Toolbox}},
url = {https://github.com/open-mmlab/mmediting},
version = {0.13.0},
year = {2022}
}

MMEditing Contributors. (2022). MMEditing: OpenMMLab Image and Video Editing Toolbox (Version 0.13.0) [Computer software]. https://github.com/open-mmlab/mmediting