Add Upgrade information in the README.

README.rdoc

@@ -41,6 +41,17 @@ This library is intended to be installed as a Gem.
 You might need administrator privileges on your system to install it.
 
 
+== Upgrade
+
+Install the newer version via RubyGems.
+
+  $ gem install whois
+
+Minor and bugfix releases normally won't break backwards-compatibility. You can read the CHANGELOG.rdoc file to learn about the changes in each release.
+
+Read the {Upgrading}[http://www.ruby-whois.org/manual/upgrading.html] documentation page for detailed information about incompatible changes and further instructions.
+
+
 == Getting Started
 
 Note. This section covers only the essentials for getting started with the Whois library. The {documentation}[http://www.ruby-whois.org/documentation.html] provides a more accurate explanation including tutorials, more examples and technical details about the client/server/record/parser architecture.