[ISSUE #130] Add explanation how to solve 'controller-gen: No such file or directory question' in READE.md

[koalawangyang]

What is the purpose of the change

Add explanation how to solve 'controller-gen: No such file or directory question' in READE.md

Brief changelog

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Verifying this change

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[koalawangyang]

@caigy sorry for my late PR, just have time to do this. Hope this could be helpful.