update doc

  - easy to write build file.

    human readable.

    with proper abstraction.

    - build system must be extensible.

      user can build any kind of projects. user just need to describe how

      files are related and which command can build which file.

    - easy to update existing projects when build template (p-p-t) has updated.

      essentially there should be abstraction so that only project related

      value is listed in user build file.

      other build logic should be abstracted.

  - build fast.

    do not do unnecessary checks.

    for example, when no .py file or python venv change, pylint should not run

    side note: I don't think I need deb when building using docker.

    install via deb just slow down the build and doesn't provide much value.

  - 

** 2019-02-28 add support for running application test using docker-compose.

see ~/websites/url-alias project for an example.