Proposal to add some 'cookbook' docker files

The jenkins image is great, but to make it useful:
1. you have to install plugins, its odd git/maven are not standard. (its a bit of work to find the plugins you have installed and get the right file format, see #206, #207
2. If you modify the volume, by copying files you have to use some other standard patterns in your docker file to get the permissions right. (I'm my example I added some jobs for creating a demo.) Ie you have to change the entry point and install gosu to get it all working

All of these things are standard docker stuff but having a more complete cookbook with example files will help people move faster if they are not docker experts

Example: https://github.com/capitalone/Hygieia/tree/master/test-servers/jenkins

@rtyler as we discussed at the meet up tonight