Added conversations README

Conversations
=====

Lists conversations in your visibility scope

```Ruby
  conversation_collection = client.conversation(:index)
  conversation = conversation_collection.all
```

You can also filter by multiple params (see docs [here](https://redbooth.com/api/api-docs/#page:conversations,header:conversations-conversations-list) )

```Ruby
  filtered_conversations = client.conversation(:index, order: 'id-DESC',
                                                       per_page: 50,
                                                       project_id: 123)
```

Fetch a especific conversation

```Ruby
  conversation = client.conversation(:show, id: 123)
```

Update a especific conversation

```Ruby
  conversation = client.conversation(:update, id: 123, name: 'new name')
```

Delete a especific conversation

```Ruby
  client.conversation(:delete, id: 123)
```