Update README.

README.md

@@ -3,6 +3,56 @@
 [Passport](https://github.com/jaredhanson/passport) strategy for authenticating
 with [Google](http://www.google.com/) using OpenID 2.0.
 
+## Installation
+
+    $ npm install passport-google
+
+## Usage
+
+#### Configure Strategy
+
+The Google authentication strategy authenticates users using a Google account,
+which is also an OpenID 2.0 identifier.  The strategy requires a `validate`
+callback, which accepts this identifier and calls `done` providing a user.
+Additionally, options can be supplied to specify a return URL and realm.
+
+    passport.use(new GoogleStrategy({
+        returnURL: 'http://localhost:3000/auth/google/return',
+        realm: 'http://localhost:3000/'
+      },
+      function(identifier, done) {
+        User.findByOpenID({ openId: identifier }, function (err, user) {
+          return done(err, user);
+        });
+      }
+    ));
+
+#### Authenticate Requests
+
+Use `passport.authenticate()`, specifying the `'google'` strategy, to
+authenticate requests.
+
+For example, as route middleware in an [Express](http://expressjs.com/)
+application:
+
+    app.get('/auth/google',
+      passport.authenticate('google'),
+      function(req, res){
+        // The request will be redirected to Google for authentication, so
+        // this function will not be called.
+      });
+
+    app.get('/auth/google/callback', 
+      passport.authenticate('google', { failureRedirect: '/login' }),
+      function(req, res) {
+        // Successful authentication, redirect home.
+        res.redirect('/');
+      });
+
+#### Examples
+
+For a complete, working example, refer to the [signon example](https://github.com/jaredhanson/passport-google/tree/master/examples/signon).
+
 ## Credits
 
   - [Jared Hanson](http://github.com/jaredhanson)