They have [0][1] ("beta" was dropped from the v4 releases at v4.0.0), and are actually in the process of updating the documentation [2]. It's just odd to do that after a release.
Whoops, guess it's a good idea to check things before blurting something out.
In that case I'm not sure what's best, to let newcomers in on the new goodies of v4 or to avoid confusing previous users.
[0] https://www.npmjs.com/package/webpack
[1] https://github.com/webpack/webpack/releases
[2] https://github.com/webpack/webpack.js.org/pull/1905