Show webpack 2 config example in docs: rules not loaders

[Stupidism]

Issue:
It took me 2 hours to figure it out how to config webpack in the new version.
All I wanted is something like this. But I'm not familiar with webpack breaking changes.

const path = require('path');

module.exports = {
  module: {
    rules: [
      {
        test: /\.md$/,
        loaders: ['raw-loader'],
        include: path.resolve(__dirname, '../'),
      },
    ],
  },
};

What I did

changed module.loaders into module.rules in docs/**/custome-webpack-config.md

How to test

[shilman]

Thanks! @ndelangen this needs to go in #1093 migration guide for sure!

[codecov]

Codecov Report

Merging #1137 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1137   +/-   ##
=======================================
  Coverage   12.86%   12.86%           
=======================================
  Files         198      198           
  Lines        4501     4501           
  Branches      715      715           
=======================================
  Hits          579      579           
  Misses       3289     3289           
  Partials      633      633

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[shilman]

@Stupidism sorry for the trouble. We are hustling to document the changes for 3.0 before the release, so things are a little inconsistent for the next couple days. Thanks so much for your contribution! 👍