Automation can range from getting a notification, to factory automation (Process Control), depending on the context.
For this automation to work, your workspace should be setup correctly
workspace (folder)
automation (folder) -> clone above git project into this folder
organizations (folder)
organization name (folder)
admin (folder)
projects (folder)
project name (folder)
builds (folder)
version XXX (folder)
project-name-platform (folder)
repositories (folder)
project-name-platform (folder)
Source code
References
https://effectiveunity.com/articles/making-most-of-unitys-command-line/
https://discuss.bitrise.io/t/how-to-build-a-unity-project/1317