fix(readme): correct installation instructions

README.md

@@ -17,15 +17,26 @@ After [enabling Greenkeeper for your repository](https://github.com/greenkeeperi
 
 1. [Create a GitHub access token with push access to your repository](https://github.com/settings/tokens) and make it available to Travis CI's environment as `GH_TOKEN`.
 
-1. Configure Travis CI to run `greenkeeper-shrinkwrap-update` right before it `npm install`s your dependencies.
+1. Configure Travis CI to use the npm version you want your shrinkwrap files to be generated with before it `npm install`s your dependencies.
+
+  ```yml
+  before_install:
+  # It is advisable to use latest npm, as there are a lot of shrinkwrap fixes in there
+  - npm install -g npm
+  ```
+
+1. Install `greenkeeper-shrinkwrap` as well.
 
   ```yml
   before_install:
-  # Note that this plugin uses the installed npm's built-in mechanism to update the shrinkwrap
-  # Therefor it is advisable to use latest npm, as there are quite some shrinkwrap fixes in there
   - npm install -g npm
   - npm install -g greenkeeper-shrinkwrap@1
-  - greenkeeper-shrinkwrap-update
+  ```
+
+1. Configure Travis CI to run `greenkeeper-shrinkwrap-update` right before it executes your tests.
+
+  ```yml
+  before_script: greenkeeper-shrinkwrap-update
   ```
 
 1. Configure Travis CI to run `greenkeeper-shrinkwrap-upload` right after it executed your tests.
@@ -34,8 +45,6 @@ After [enabling Greenkeeper for your repository](https://github.com/greenkeeperi
   after_script: greenkeeper-shrinkwrap-upload
   ```
 
-That's it.
-
 ### Testing multiple node versions
 
 It is common to test multiple node versions and therefor have multiple test jobs for one build. In this case the shrinkwrap will automatically be updated for every job, but only uploaded for the first one.
@@ -47,7 +56,7 @@ node_js:
 before_install:
 - npm install -g npm
 - npm install -g greenkeeper-shrinkwrap@1
-- greenkeeper-shrinkwrap-update
+before_script: greenkeeper-shrinkwrap-update
 # Only the node version 6 job will upload the shrinkwrap
 after_script: greenkeeper-shrinkwrap-upload
 ```