fill out readme with usage details

Author: chrisbreiding

README.md

@@ -2,14 +2,128 @@
 
 Cypress preprocessor for bundling JavaScript via browserify
 
-## Install
+## Installation
 
 Requires [Node](https://nodejs.org/en/) version 6 or above.
 
 ```sh
-npm install --save-dev cypress-browserify-preprocessor
+npm install --save-dev @cypress/browserify-preprocessor
 ```
 
+## Usage
+
+In your project's [plugins file](https://on.cypress.io/guides/plugins):
+
+```javascript
+const browserify = require('@cypress/browserify-preprocessor')
+
+module.exports = (register, config) => {
+  register('on:spec:file:preprocessor', browserify(config))
+}
+```
+
+## Options
+
+Pass in options as the second argument to `browserify`:
+
+```javascript
+module.exports = (register, config) => {
+  const options = {
+    extensions: [],
+    watchOptions: {},
+    transforms: [],
+    onBundle () {},
+  }
+
+  register('on:spec:file:preprocessor', browserify(config, options))
+}
+```
+
+### extensions
+
+Array of file extensions to supported.
+
+**Default**:
+
+```javascript
+['.js', '.jsx', '.coffee', '.cjsx']
+```
+
+### watchOptions
+
+Object of options passed to [watchify](https://github.com/browserify/watchify#options)
+
+**Default**:
+
+```javascript
+{
+  ignoreWatch: [
+    '**/.git/**',
+    '**/.nyc_output/**',
+    '**/.sass-cache/**',
+    '**/bower_components/**',
+    '**/coverage/**',
+    '**/node_modules/**',
+  ],
+}
+```
+
+### transforms
+
+Array of transforms. Each item is an object with a `transform` set to the path to a transform package or the required module itself and `options` set to the options for that transform.
+
+**Default**:
+
+```javascript
+[
+  {
+    transform: 'cjsxify',
+    options: {},
+  },
+  {
+    transform: 'babelify',
+    options: {
+      ast: false,
+      babelrc: false,
+      plugins: ['babel-plugin-add-module-exports'],
+      presets: ['babel-preset-env', 'babel-preset-react'],
+    },
+  },
+]
+```
+
+### onBundle
+
+A function that is called with the [browserify bundle](https://github.com/browserify/browserify#browserifyfiles--opts). This allows you to specify external files and plugins. See the [browserify docs](https://github.com/browserify/browserify#baddfile-opts) for methods available.
+
+```javascript
+browserify({
+  onBundle (bundle) {
+    bundle.external('react')
+    bundle.plugin('some-plugin')
+  }
+})
+```
+
+## Modifying default options
+
+The default options are provided as `browserify.defaultOptions` so they can be more easily modified.
+
+If, for example, you want to update the options for the `babelify` transform to turn on `babelrc`, you could do the following:
+
+```javascript
+const browserify = require('@cypress/browserify-preprocessor')
+
+module.exports = (register, config) => {
+  const options = browserify.options
+  options.transforms[1].options.babelrc = true
+
+  register('on:spec:file:preprocessor', browserify(config, options))
+}
+```
+
+**Default**: `undefined`
+
 ## License
 
 This project is licensed under the terms of the [MIT license](/LICENSE.md).