some code is missing in quick_start.md

[bazige]

in vega/docs/cn/developer/quick_start.md

@NetworkFactory.register(NetTypes.CUSTOM)

    def __init__(self, desc):
        super(SimpleCnn, self).__init__()

it may be missing this code：
class SimpleCnn(nn.Module):

[zhangjiajin]

Yes. The code in the documentation lacks the definition of the class. Thank you for discovering this error. @bazige