Correct link for troubleshooting react-dev-tools (#16690)

[liady]

As pointed out in #16690 - the link for 'React Tab Doesn't Show Up' points to the empty README.MD.
This points it to that section in the v3 version README.MD - until an updated section will be added to the new dev-tools.

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[bvaughn]

Hi 👋

Thanks for the PR, but like I mentioned on the issue originally- the link should point to this repo (https://github.com/facebook/react/tree/master/packages/react-devtools) as the new DevTools lives here. Linking to the old one would probably just cause confusion.

Seems like maybe we need to add a troubleshooting section to the README in this repo. Interested in copying that over?

[liady]

@bvaughn Hi,
I now added the section to the README file (updated the screenshot as well), and fixed the link to point there.

[bvaughn]

Thanks~