add some exercises

exercises/done/hello.rb

@@ -0,0 +1,21 @@
+#!/usr/bin/env ruby
+
+class Hello
+  def hello(name)
+    puts "Hello #{name}!"
+  end
+
+  def hello_everybody(names)
+    names.each do |name|
+      hello(name)
+    end
+  end
+end
+
+greeter = Hello.new
+
+greeter.hello("Biblo")
+
+puts
+
+greeter.hello_everybody(["Pipin", "Merry", "Sam"])