README
The included code is the source, minus supporting infrastructure for a Jenkins plug-in.
For this to work on your own computer you need a few things.

First, the project layout for a Jenkins plug-in.
Follow the instructions from the Jenkins' site on how to set that up.
https://jenkins.io/doc/developer/tutorial/prepare/
This will walk you through installing the JDK and Maven in the first step.
In the second step, follow the instructions and use the following when prompted.
groupId: io.jenkens.plugins.sample
artifactId: ranked-bug-files
The rest can be left as defaults.
Before running in step 3, go to the ranked-bug-files/src/main directory.
Once there, delete the java and resources directories.
Clone the source files from this github repo into that directory.
Move the pom.xml and stop_words.txt out two layers to the ranked-bug-files folder and replace
the pom.xml there.
The project should now be ready to run using 'mvn hpi:run' in the ranked-bug-files
directory.
To see the jenkins plugin navigate to a web browser and go to the following address.
http://localhost:8080/jenkins/

Now, the plugin is working, but unless you have a project already in mind to point it
at then you'll need one other thing and that's code with bug reports.  I used
the Defects4J command line tool for testing purposes.
https://github.com/rjust/defects4j
This page includes instructions on how to install the tool and run it.
You'll need to checkout a buggy project to the directory of your chosing.
Also, you'll need to get the bug information for the source code you obtained.
Both things are laid out under 'Using Defect4J' on the site.

Finally, to test the plugin create a new freestyle project in Jenkins.
Go to the build configure page and you should see a section for my plug-in.
Enter the directory of the source code you want to be searched.
Enter the bug report for the bug you wish to find.
Now, when you build the plugin navigate to the Bug Ranking section.
Listed there is the top 5 matching source files for the bug report.