improve Jenkins / CI docs

[ryanj]

• Add notes on how to set up CI for GitHub projects.
• Add a list of recommended plugins, explain how to use them
• Advanced config: Set Timezone - rhc set-env JAVA_OPTS_EXT="-Duser.timezone=Europe/London" -a myapp

[rimolive]

One other important thing is explain Jenkins build workflow, how it does rolling deployments, etc. so people can understand better how use this tool to avoid downtime in their apps.