README.md in adapter-mongo-0.5.5 vs README.md in adapter-mongo-0.5.6

@@ -20,9 +20,45 @@
 puts 'Should be nil: ' + adapter.read('foo').inspect
 
 puts 'Should be bar: ' + adapter.fetch('foo', 'bar')
 ```
 
+## Flavors
+
+There are two adapters included with this gem -- `:mongo` and `:mongo_atomic`. `:mongo` assumes that you are writing the full document each time. `:mongo_atomic` allows for partially updating documents. The difference is best shown with a bit of code.
+
+```ruby
+require 'adapter/mongo_atomic'
+
+key            = BSON::ObjectId.new
+full_doc       = {'a' => 'c', 'b' => 'd'}
+partial_doc    = {'a' => 'z'}
+client         = Mongo::Connection.new.db('adapter')['testing']
+adapter        = Adapter[:mongo].new(client)
+atomic_adapter = Adapter[:mongo_atomic].new(client)
+
+adapter.clear
+atomic_adapter.clear
+
+adapter.write(key, full_doc)
+adapter.write(key, partial_doc)
+
+doc = adapter.read(key)
+doc.delete('_id')
+
+# full doc must always be written with :mongo adapter
+puts 'Should be {"a"=>"z"}: ' + doc.inspect
+
+atomic_adapter.write(key, full_doc)
+atomic_adapter.write(key, partial_doc)
+
+doc = atomic_adapter.read(key)
+doc.delete('_id')
+
+# partial updates can be written with atomic adapter as $set is used
+puts 'Should be {"a"=>"z", "b"=>"d"}: ' + doc.inspect
+```
+
 See examples/ or specs/ for more usage.
 
 ## Contributing
 
 * Fork the project.