docs: add installation instructions and gem version (#16)

Author: laurmurclar

README.md

@@ -1,6 +1,39 @@
 # GraphitiSpecHelpers
 
 ![Build Status](https://travis-ci.org/graphiti-api/graphiti_spec_helpers.svg?branch=master)
+[![Gem Version](https://badge.fury.io/rb/graphiti_spec_helpers.svg)](https://badge.fury.io/rb/graphiti_spec_helpers)
 
 Spec helpers for [Graphiti](https://github.com/graphiti-api/graphiti)
 APIs.
+
+# Installation
+Note: this assumes you have [rspec-rails](https://github.com/rspec/rspec-rails) installed & configured already.
+
+`Gemfile`
+```ruby
+group :development, :test do
+  # ...
+  gem 'graphiti_spec_helpers', '~> 1.1'
+  # ...
+end
+```
+
+`spec/rails_helper.rb`
+```ruby
+# ...
+# Add additional requires below this line. Rails is not loaded until this point!
+require 'graphiti_spec_helpers/rspec'
+# ...
+
+RSpec.configure do |config|
+  # ...
+  config.include GraphitiSpecHelpers::RSpec
+  config.include GraphitiSpecHelpers::Sugar
+  config.include Graphiti::Rails::TestHelpers
+  # ...
+```
+
+Then in your project directory
+```sh
+$ bundle install
+```