Merge pull request #683 from jjb/aws-sdk-documentation

Add documentation for including `aws-sdk` in Gemfile

README.md

@@ -164,9 +164,14 @@ file at
 _**NOTE**: This is a change from previous versions of Paperclip, but is overall a
 _**NOTE**: This is a change from previous versions of Paperclip, but is overall a
 safer choice for the default file store._
 safer choice for the default file store._
 
 
-You may also choose to store your files using Amazon's S3 service. You can find
-more information about S3 storage at the description for
-[`Paperclip::Storage::S3`](http://rubydoc.info/gems/paperclip/Paperclip/Storage/S3).
+You may also choose to store your files using Amazon's S3 service. To do so, include
+the `aws-sdk` gem in your Gemfile:
+
+    gem 'aws-sdk'
+
+And then you can specify using S3 from `has_attached_file`. 
+You can find more information about configuring and using S3 storage in
+[the `Paperclip::Storage::S3` documentation](http://rubydoc.info/gems/paperclip/Paperclip/Storage/S3).
 
 
 Files on the local filesystem (and in the Rails app's public directory) will be
 Files on the local filesystem (and in the Rails app's public directory) will be
 available to the internet at large. If you require access control, it's
 available to the internet at large. If you require access control, it's

lib/paperclip/storage/s3.rb

@@ -2,6 +2,9 @@ module Paperclip
   module Storage
   module Storage
     # Amazon's S3 file hosting service is a scalable, easy place to store files for
     # Amazon's S3 file hosting service is a scalable, easy place to store files for
     # distribution. You can find out more about it at http://aws.amazon.com/s3
     # distribution. You can find out more about it at http://aws.amazon.com/s3
+    #
+    # To use Paperclip with S3, include the +aws-sdk+ gem in your Gemfile:
+    #   gem 'aws-sdk'
     # There are a few S3-specific options for has_attached_file:
     # There are a few S3-specific options for has_attached_file:
     # * +s3_credentials+: Takes a path, a File, or a Hash. The path (or File) must point
     # * +s3_credentials+: Takes a path, a File, or a Hash. The path (or File) must point
     #   to a YAML file containing the +access_key_id+ and +secret_access_key+ that Amazon
     #   to a YAML file containing the +access_key_id+ and +secret_access_key+ that Amazon