Improve user instruction

[130s]

Some complaints feedback from active users, e.g. https://github.com/ros-industrial-consortium/bezier/issues/153

Indeed README gets necessarily but surely complexed.

• [x] Add more sample config --> #113
• [x] provide a template .travis.yml content so that users simply download in their .travis.yml. -> #337
• [x] The quickstart config is a little bit outdated and not really complete (#336). -> addressed in https://github.com/ros-industrial/industrial_ci/pull/337
• [x] Dissect README into pieces per level https://github.com/ros-industrial/industrial_ci/issues/105#issuecomment-273318237 --> #113
• [ ] DOCKER_PULL usage https://github.com/ros-industrial/industrial_ci/pull/283#discussion_r201809566
• [x] This link is broken in CATKIN_CONFIG. -> done https://github.com/ros-industrial/industrial_ci/issues/105#issuecomment-443870126

[mathias-luedtke]

Pehaps we should split README.md into different chapters (-> doc directory). And start with a TL;DR section with a minimal example:

sudo: required 
dist: trusty 
language: generic 
env:
  - ROS_DISTRO="indigo"
install:
  - git clone --depth 1 https://github.com/ros-industrial/industrial_ci.git .ci_config  
script: 
  - .ci_config/travis.sh

[VictorLamoine]

Complaint is a strong word. You have done some awesome work with this repository. Please don't feel offended :hugs:

[130s]

@VictorLamoine Thanks. I've seen "complaint" in OSS is often used as the same meaning as "feedback", and that was what I meant ;)

[mathias-luedtke]

A template might help preventing issues like #254

[130s]

• provide a template .travis.yml content so that users simply download in their .travis.yml.

Template being added to https://github.com/ros-industrial/industrial_ci/pull/234

[mathias-luedtke]

The quickstart config is a little bit outdated and not really complete (#336).

[130s]

• [ ] This link is broken in CATKIN_CONFIG.

Can't find "optional-customize-catkin-config" section. And customize-catkin-config section link is working. Checked.