spree extension generator: updated README.md

cmd/lib/spree_cmd/templates/extension/README.md

@@ -3,24 +3,31 @@
 
 Introduction goes here.
 
-Installation
-------------
+## Installation
 
-Add <%= file_name %> to your Gemfile:
+1. Add this extension to your Gemfile with this line:
+  ```ruby
+  gem '<%= file_name %>', github: '[your-github-handle]/<%= file_name %>', branch: 'X-X-stable'
+  ```
 
-```ruby
-gem '<%= file_name %>'
-```
+  The `branch` option is important: it must match the version of Spree you're using.
+  For example, use `3-1-stable` if you're using Spree `3-1-stable` or any `3.1.x` version.
 
-Bundle your dependencies and run the installation generator:
+2. Install the gem using Bundler:
+  ```ruby
+  bundle install
+  ```
 
-```shell
-bundle
-bundle exec rails g <%= file_name %>:install
-```
+3. Copy & run migrations
+  ```ruby
+  bundle exec rails g <%= file_name %>:install
+  ```
 
-Testing
--------
+4. Restart your server
+
+  If your server was running, restart it so that it can find the assets properly.
+
+## Testing
 
 First bundle your dependencies, then run `rake`. `rake` will default to building the dummy app if it does not exist, then it will run specs. The dummy app can be regenerated by using `rake test_app`.
 
@@ -36,4 +43,11 @@ Simply add this require statement to your spec_helper:
 require '<%= file_name %>/factories'
 ```
 
+
+## Contributing
+
+If you'd like to contribute, please take a look at the
+[instructions](CONTRIBUTING.md) for installing dependencies and crafting a good
+pull request.
+
 Copyright (c) <%= Time.now.year %> [name of extension creator], released under the New BSD License