Minimum requirements when manually installing a Jenkins server

[michaelin]

I've tried running the katas on a Jenkins instance installed using apt. There are a few prerequisites that might be worth mentioning in setup-on-your-own.md.

1. Docker must be available on the server and/or worker instance
2. The user running Jenkins ("jenkins" user by default) must be added to the Docker group
3. Ensure the Blue Ocean plugin is installed. It isn't installed by default or as part of the recommended plugins in a manually installed Jenkins instance.

[sofusalbertsen]

That would be great, can you add that to the setup?