Fix document

[fwh1990]

Description

See section Webpack Plugin in README.md

{
    test: /\.js$/,
    include: /node_modules\/react-dom/,
    use: ['react-hot-loader/webpack']
}

Expected behavior

Change property include to /node_modules[\\\/]react-dom/, the reason is you should compatible with unix and window.

Actual behavior

Only compatible with unix