Document $conf['jenkins_base_url']

In order to point this module at your jenkins installation you'll likely need to set the $conf['jenkins_base_url'] variable in your settings.php file. It would probably be good to add something like the following to the README.

Usage:
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You need to tell the module where your Jenkins installation lives. This can be
done by setting the 'jenkins_base_url' variable in your settings.php file. e.g.)

$conf['jenkins_base_url'] = http://jenkins.example.com';

By default this is set to 'http://localhost:8080'.