Steps to reproduce the problem:
1. .
2. 
3. 

What is the expected behavior?

What went wrong?
After I download the source code, when I run gn.by 
wrong:
gn.py: Could not find checkout in any parent of the current path.
This must be run inside a checkout.

I just get the code from the github, so how can I solve this problem?

Did this work before? N/A 

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