Document IAM Profile AWS S3 configuration key.

doc/raketasks/backup_restore.md

@@ -79,6 +79,9 @@ gitlab_rails['backup_upload_connection'] = {
   'region' => 'eu-west-1',
   'aws_access_key_id' => 'AKIAKIAKI',
   'aws_secret_access_key' => 'secret123'
+  # If using an IAM Profile, leave aws_access_key_id & aws_secret_access_key empty
+  # ie. 'aws_access_key_id' => '',
+  # 'use_iam_profile' => 'true'
 }
 gitlab_rails['backup_upload_remote_directory'] = 'my.s3.bucket'
 ```
@@ -95,12 +98,16 @@ For installations from source:
         region: eu-west-1
         aws_access_key_id: AKIAKIAKI
         aws_secret_access_key: 'secret123'
+        # If using an IAM Profile, leave aws_access_key_id & aws_secret_access_key empty
+        # ie. aws_access_key_id: ''
+        # use_iam_profile: 'true'
       # The remote 'directory' to store your backups. For S3, this would be the bucket name.
       remote_directory: 'my.s3.bucket'
       # Turns on AWS Server-Side Encryption with Amazon S3-Managed Keys for backups, this is optional
       # encryption: 'AES256'
 ```
+
 If you are uploading your backups to S3 you will probably want to create a new
 IAM user with restricted access rights. To give the upload user access only for
 uploading backups create the following IAM profile, replacing `my.s3.bucket`