Add docs for Rollbar::Middleware::Rack

[skip ci]

README.md

@@ -62,6 +62,31 @@ $ heroku config:add ROLLBAR_ACCESS_TOKEN=POST_SERVER_ITEM_ACCESS_TOKEN
 That's all you need to use Rollbar with Rails.
 
 
+### Sinatra
+
+Initialize Rollbar with your access token somewhere during startup:
+
+```ruby
+Rollbar.configure do |config|
+  config.access_token = 'POST_SERVER_ITEM_ACCESS_TOKEN'
+  # other configuration settings
+  # ...
+end
+```
+
+Then mount the middleware in your app, like:
+
+```ruby
+require 'rollbar/middleware/sinatra'
+
+class MyApp < Sinatra::Base
+  use Rollbar::Middleware::Sinatra
+  # other middleware/etc
+  # ...
+end
+```
+
+
 ### Rack
 
 Initialize Rollbar with your access token somewhere during startup:
@@ -77,28 +102,22 @@ end
 <!-- RemoveNextIfProject -->
 Be sure to replace ```POST_SERVER_ITEM_ACCESS_TOKEN``` with your project's ```post_server_item``` access token, which you can find in the Rollbar.com interface.
 
-This monkey patches `Rack::Builder` to work with Rollbar automatically.
-
-For more control, disable the monkey patch:
+The gem monkey patches `Rack::Builder` so Rollbar reports will be sent automatically without any other action. If you prefer to disable the monkey patch apply this change to your config:
 
 ```ruby
 Rollbar.configure do |config|
-  config.disable_monkey_patch = true
+  config.disable_rack_monkey_patch = true
   # other configuration settings
   # ...
 end
 ```
 
-Then mount the middleware in your app, like:
+If you disabled the `Rack::Builder` monkey patch or it doesn't work for the Rack framework you are using, then add our Rack middleware to your app:
 
 ```ruby
-require 'rollbar/middleware/sinatra'
+require 'rollbar/middleware/rack
 
-class MyApp < Sinatra::Base
-  use Rollbar::Middleware::Sinatra
-  # other middleware/etc
-  # ...
-end
+use Rollbar::Middleware::Rack
 ```
 
 ### Plain Ruby
@@ -371,6 +390,8 @@ end
 
 # You can add the middleware to your application, for example:
 
+require 'rollbar/middleware/sinatra'
+
 class App < Sinatra::Base
   use Rollbar::Middleware::Sinatra
   use RollbarPersonData