Improve documentation

[epegzz]

As mentioned by @franciscolourenco in #32 🙏 the documentation could use some update to include the recommended way of configuring webpack with vue.js.

// vue.config.js
module.exports = {
	chainWebpack: config => {
		const moduleTypes = ['vue-modules', 'vue', 'normal-modules', 'normal']
		moduleTypes.forEach(type =>
			config.module
				.rule('scss')
				.oneOf(type)
				.use('@epegzz/sass-vars-loader')
				.loader('@epegzz/sass-vars-loader')
				.options({
					syntax: 'scss',
					files: [path.resolve(__dirname, './src/styles/colors.js')],
				})
		)
	},
}

Originally posted by @franciscolourenco in #32 (comment)