react-scripts readme "npm run build fails to minify" section after v2

[sag1v]

Is this a bug report?

No

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Now that v2 compiles node_modues this section in readme should be updated.

@gaearon suggested to write "migrate to 2.x" .

Should we keep the current text as well (for legacy users)?
What about a link to a guide for migrating?

[Timer]

closing in favor of PR