Build out README

Author: derrickreimer

README.md

@@ -1,6 +1,6 @@
 # Drip Ruby Bindings
 
-TODO: Write a gem description
+A Ruby toolkit for the [Drip](https://www.getdrip.com/) API.
 
 ## Installation
 
@@ -18,7 +18,55 @@ Or install it yourself as:
 
 ## Usage
 
-TODO: Write usage instructions here
+To begin making requests, spin up a new Drip client:
+
+```ruby
+client = Drip::Client.new do |c|
+  c.api_key = "YOUR_API_TOKEN"
+  c.account_id = "YOUR_ACCOUNT_ID"
+end
+```
+
+You can find your API key [here](https://www.getdrip.com/settings/general)
+and your account ID [here](https://www.getdrip.com/settings/site).
+
+Since the Drip client is a flat API client, most API actions are available
+as methods on the client object. The following methods are currently available:
+
+| Action                     | Method                                               |
+| :------------------------- | :--------------------------------------------------- |
+| Create/update a subscriber | `#create_or_update_subscriber(email, options = {})`  |
+| Fetch a subscriber         | `#subscriber(id_or_email)`                           |
+| Subscribe to a campaign    | `#subscribe(email, campaign_id, options = {})`       |
+| Unsubscribe                | `#unsubscribe(id_or_email, options = {})`            |
+| Apply a tag                | `#apply_tag(email, tag)`                             |
+| Remove a tag               | `#remove_tag(email, tag)`                            |
+| Track an event             | `#track_event(email, action, properties = {})`       |
+
+
+**Note:** We do not yet have complete API coverage. If we are missing an API method
+that you need to use in your application, please file an issue and/or open a
+pull request.
+
+## Examples
+
+```ruby
+client = Drip::Client.new do |c|
+  c.api_key = "YOUR_API_TOKEN"
+  c.account_id = "YOUR_ACCOUNT_ID"
+end
+
+# Fetch a subscriber
+resp = client.subscriber("foo@example.com")
+# => <Drip::Response ...>
+
+resp.success?
+# => true
+
+subscriber = resp.subscribers.first
+subscriber.email
+# => "foo@example.com"
+```
 
 ## Contributing