Update README to reflect --init changes

So users are aware that the --init will also create a Gemfile.next.lock.

Author: fbuys

README.md

@@ -83,7 +83,7 @@ Right now, the path to the shitlist is hardcoded so make sure you store yours at
 This command helps you dual-boot your application.
 
 ```bash
-next --init         # Create Gemfile.next
+next --init         # Create Gemfile.next and Gemfile.next.lock
 vim Gemfile         # Tweak your dependencies conditionally using `next?`
 next bundle install # Install new gems
 next rails s        # Start server using Gemfile.next
@@ -105,6 +105,17 @@ Or install it yourself as:
 
     $ gem install next_rails
 
+## Setup
+
+Execute:
+
+    $ next --init
+
+Init will create a Gemfile.next and an initialized Gemfile.next.lock.
+The Gemfile.next.lock is initialized with the contents of your existing 
+Gemfile.lock lock file. We initialize the Gemfile.next.lock to prevent
+major version jumps when running the next version of Rails.
+
 ## License
 
 The gem is available as open source under the terms of the [MIT License](https://opensource.org/licenses/MIT).