Add post-install message

Rakefile

@@ -36,6 +36,24 @@ spec = Gem::Specification.new do |s|
   s.add_development_dependency "rspec", "~> 2.9.0"
   s.add_development_dependency "mocha"
   s.add_development_dependency "yard"
+
+  s.post_install_message = <<EOS
+********************************************************************************
+
+  Thank you for installing the whois gem!
+
+  If you like this gem, please support the project.
+  http://pledgie.com/campaigns/11383
+
+  Does your project or organization use this gem? Add it to the apps wiki.
+  https://github.com/weppos/whois/wiki/apps
+
+  Are you looking for a quick and convenient way to perform WHOIS queries?
+  Check out RoboWhois WHOIS API.
+  http://www.robowhois.com/
+
+********************************************************************************
+EOS
 end