Improve user instruction

[130s]

Some complaints feedback from active users, e.g. ros-industrial-attic/bezier#153

Indeed README gets necessarily but surely complexed.

• Add more sample config --> [doc] Split readme into quick start and detail. #113
• provide a template .travis.yml content so that users simply download in their .travis.yml. -> Improve Travis template #337
• The quickstart config is a little bit outdated and not really complete ([Melodic/Bionic] Docker, command not found #336). -> addressed in Improve Travis template #337
• Dissect README into pieces per level Improve user instruction #105 (comment) --> [doc] Split readme into quick start and detail. #113
• DOCKER_PULL usage Add DOCKER_PULL option #283 (comment)
• This link is broken in CATKIN_CONFIG. -> done Improve user instruction #105 (comment)

[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 🤗

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The quickstart config is a little bit outdated and not really complete (#336).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