Add documentation about job parameter

[Shmuma]

After upgrade to 2.5.0, I get the following error

[ERROR] Failed to execute goal com.exasol:project-keeper-maven-plugin:4.5.0:fix (default-cli) on project cloud-storage-extension: Execution default-cli of goal com.exasol:project-keeper-maven-plugin:4.5.0:fix failed: E-PK-CORE-208: Missing job in step customization of workflow 'ci-build.yml' in file '.project-keeper.yml'. Add job with one of the following values: ['matrix-build', 'next-java-compatibility', 'build', 'start_release']. -> [Help 1]
[ERROR] 

Was fixed by adding job: matrix-build to the ci customizations parameters, but it wasn't described in documentation.
It would be great to document this.