For the latest ("edge") stuff, instruct the bundler to get the gem straight from github:
gem 'netzke-core', :git => "git://github.com/nomadcoder/netzke-core.git"
Netzke assumes that your Ext JS library is located in public/extjs. It can be a symbolic link, e.g.:
public/extjs
ln -s ~/code/sencha/ext-4.0.0 public/extjs
(Make sure that the location of the license.txt file is exactly public/extjs/license.txt)
public/extjs/license.txt
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