Added the installation instructions for Ubuntu

Author: homer6

README.markdown

@@ -22,6 +22,16 @@ Old school:
     chmod 755 gist &&
     mv gist /usr/local/bin/gist
 
+Ubuntu:
+
+    sudo apt-get install ruby
+    sudo apt-get install rubygems
+    sudo apt-get install libopenssl-ruby
+    sudo gem install gist
+    sudo cp /var/lib/gems/1.8/bin/gist /usr/local/bin/
+    gist -h
+
+
 
 Use
 ---