The build process should be simplified:

• Scripts for AppVeyor and Tracis CI should not be the scripts used for building explained "up front". This is not intuitive.
• The documentation should be easier to follow for a new developer that want to start working on the project.
• Users runs on Linux , Windows or macOS and are usually expecting different build instructions specific for their OS. The best option to follow this rule would be to create linux and windows directories under /ci directory. Each directory should contains the required scripts for these operating systems.
• Try to have "one click build".