Update README.md with usage instructions

README.md

@@ -7,3 +7,48 @@
 JS client authentication library for [Solid](https://github.com/solid/solid)
 browser-based clients. Used inside
 [`solid-client`](https://github.com/solid/solid-client).
+
+## Usage
+
+The `solid-auth-tls` client can be used from Node as well as browser processes.
+
+### Within Node
+
+```js
+const auth = require('solid-auth-tls')
+
+auth.login({ key: 'path/to/tls-key.pem', cert: 'path/to/tls-cert.pem' })
+  .then(webId => /* ... */)
+  .catch(err => /* ... */)
+```
+
+### Within the Browser
+
+A UMD bundle is provided so that you can do the following (after including the
+bundle via an HTML `<script>` tag):
+
+```js
+SolidAuthTLS.login() // the browser automatically provides the client key/cert for you
+  .then(webId => /* ... */)
+  .catch(err => /* ... */)
+```
+
+You can also use a module bundler such as webpack and require the module like in
+the node example.  When using webpack you need to include the following
+plugin(s) in order to keep webpack from trying to resolve node modules such as
+`fs` and `https`.  Add this to your `webpack.config.js`:
+
+```js
+const webpack = require('webpack')
+
+module.exports = {
+  // ...
+  plugins: [
+    new webpack.DefinePlugin({ 'global.IS_BROWSER': true })
+    new webpack.optimize.UglifyJsPlugin(/* ... */)
+  ]
+}
+```
+
+This makes sure that code paths that require node modules (for use within node)
+become dead code and get removed by the `UglifyJsPlugin`'s dead code eliminator.