add who example

bindings/ruby/examples/who.rb

@@ -0,0 +1,13 @@
+require 'rbsigar'
+
+def format_time(who)
+  return Time.at(who.time).strftime("%b %e %H:%M")
+end
+
+sigar = Sigar.new
+
+whos = sigar.who_list
+
+whos.each do |who|
+  puts who.user + "\t" + who.device + "\t" + format_time(who) + who.host
+end