Add ruby example

docs/sdks/ruby/example-list-buckets.rb

@@ -0,0 +1,10 @@
+#!/usr/bin/env ruby
+require 'aws-sdk'
+
+s3 = Aws::S3::Client.new(endpoint: "http://127.0.0.1:9000/",
+                         require_https_for_sse_cpk: false,
+                         region: "minio")
+resp = s3.list_buckets
+resp.buckets.each do |bucket|
+  puts "#{bucket.name} => #{bucket.creation_date}"
+end