Fix README command

[chongkong]

ng --help 

to

ng help

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[grizzm0]

Dupe of #3159.
Please search before submitting a PR.

[chongkong]

I thought it would be such a valuable chance for contributing that I was in a bit hurry 😂 I was going to search for this issue after sending pull request, and now I found it was duplicated, I would close the PR 🤔

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