Offline Rdoc generation, howto

Recently, I wanted to work with a Ruby gem called 'devise'.

Like many people installing gems, usually I don't include their Rdoc because of the time it takes.

My Internet connection happened to be down, so for my already installed gem devise, I wanted to generate its Ruby documentation (Rdoc) offline. The documented command for this unfortunately wanted to generate the Rdoc for all my gems:
rdoc {gem-name}

This happened with these versions:
ruby 1.9.2-p290
rubygems 1.8.10
rdoc 3.12

I found this workaround to generate a single gem's Rdocs:
cd ~/.rvm/gems/{ruby-version}/gems/{gem-name}-{version}
rdoc .
mv doc/* ~/.rvm/gems/{ruby-version}/doc/{gem-name}-{version}/rdoc
cd ~
gem server
# In SeaMonkey:
open localhost:8808
click {gem-name}
click 'rdoc'

Copyright (c) 2012 Mark D. Blackwell.