docs: Documentation for migrate (#175)

* initial draft of migrate documentation

* formatting

* formatting

* added summary of migrate changes

* maintain consistent usage of user through documentation

MIGRATE.md

@@ -1 +1,161 @@
+## webpack-migrate
 
+The `migrate` feature eases the transition from [version 1](http://webpack.github.io/docs/) to [version 2](https://gist.github.com/sokra/27b24881210b56bbaff7). `migrate` 
+also allows users to switch to the new version of webpack without having to extensively [refactor](https://webpack.js.org/guides/migrating/).
+
+### Usage
+To use `migrate`, run the following command, with the value of `<config>` being a path to an existing webpack configuration file
+
+```bash
+webpack-cli migrate <config>
+```
+
+Given a basic configuration file like so:
+
+```javascript
+const ExtractTextPlugin = require('extract-text-webpack-plugin');
+const HtmlWebpackPlugin = require('html-webpack-plugin');
+const path = require('path');
+const UglifyJSPlugin = require('uglifyjs-webpack-plugin');
+const webpack = require('webpack');
+
+module.exports = {
+
+  entry: {
+	index: './src/index.js',
+	vendor: './src/vendor.js'
+  },
+
+  output: {
+	filename: '[name].[chunkhash].js',
+	chunkFilename: '[name].[chunkhash].js',
+	path: path.resolve(__dirname, 'dist')
+  },
+
+  module: {
+	loaders: [
+	  {
+		test: /\.js$/,
+		exclude: /node_modules/,
+		loader: 'babel',
+		query: {
+		  presets: ['es2015']
+		}
+	  },
+	  {
+		test: /\.(scss|css)$/,
+		loader: ExtractTextPlugin.extract('style', 'css!sass')
+	  }
+	]
+  },
+
+  plugins: [
+	new UglifyJSPlugin(),
+
+	new ExtractTextPlugin('styles-[contentHash].css'),
+
+	new webpack.optimize.CommonsChunkPlugin({
+	  name: 'common',
+	  filename: 'common-[hash].min.js'
+	}),
+
+	new HtmlWebpackPlugin()
+  ]
+
+};
+```
+
+The `migrate` command, when run, will show the proposed changes to the config file in the terminal, prompting the user to
+accept the changes or not:
+
+```bash
+$ webpack-cli migrate ./webpack.config.js
+ ✔ Reading webpack config
+ ✔ Migrating config from v1 to v2
+-     loaders: [
++     rules: [
+-         loader: 'babel',
+        query: {
++         use: [{
+          loader: 'babel-loader'
+        }],
+        options: {
+-         loader: ExtractTextPlugin.extract('style', 'css!sass')
++         use: ExtractTextPlugin.extract({
+          fallback: 'style',
+          use: 'css!sass'
+        })
+? Are you sure these changes are fine? Yes
+
+ ✔︎ New webpack v2 config file is at /Users/obuckley/Workspace/github/repos/webpack-migrate-sandbox/webpack.config.js
+```
+
+
+After it has run, we have our new webpack config file!
+
+```javascript
+const ExtractTextPlugin = require('extract-text-webpack-plugin');
+const HtmlWebpackPlugin = require('html-webpack-plugin');
+const path = require('path');
+const UglifyJSPlugin = require('uglifyjs-webpack-plugin');
+const webpack = require('webpack');
+
+module.exports = {
+
+  entry: {
+	index: './src/index.js',
+	vendor: './src/vendor.js'
+  },
+
+  output: {
+	filename: '[name].[chunkhash].js',
+	chunkFilename: '[name].[chunkhash].js',
+	path: path.resolve(__dirname, 'dist')
+  },
+
+  module: {
+	rules: [
+	  {
+		test: /\.js$/,
+		exclude: /node_modules/,
+		use: [{
+		  loader: 'babel-loader'
+		}],
+		options: {
+		  presets: ['es2015']
+		}
+	  },
+	  {
+		test: /\.(scss|css)$/,
+		use: ExtractTextPlugin.extract({
+		  fallback: 'style',
+		  use: 'css!sass'
+		})
+	  }
+	]
+  },
+
+  plugins: [
+	new UglifyJSPlugin(),
+
+	new ExtractTextPlugin('styles-[contentHash].css'),
+
+	new webpack.optimize.CommonsChunkPlugin({
+	  name: 'common',
+	  filename: 'common-[hash].min.js'
+	}),
+
+	new HtmlWebpackPlugin()
+  ]
+
+};
+```
+
+In summary, we can see the follow changes were made
+1.  The webpack schema for using loaders has changed
+    - `loaders` is now `module.rules` 
+    -  `query` is now `options`
+1.  All loaders now have to have the *loader* suffix, e.g. `babel` -> `babel-loader`
+
+**Note: This command does NOT handle updating dependencies in _package.json_, it is only a migration tool for the config
+file itself.  Users are expected to manage dependencies themselves.**