README.md Webpack config links to deprecated v1 docs

[Rrrapture]

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Thanks for the great Webpack extension!

In the last paragraph of the Step 2 Usage section of the README, "factor its configuration" links to the deprecated webpack v1
docs - https://webpack.github.io/docs/configuration.html.

What do you think about it pointing to the current Webpack site docs? https://webpack.js.org/concepts/configuration

I'm working on the pull request now.