Document scripts/enroll-users.py for Fedora CI (packit#1085)

Document `scripts/enroll-users.py` for Fedora CI

Related to packit/deployment#679
Merge after packit/deployment#679

Reviewed-by: Maja Massarini
Reviewed-by: Laura Barcziová

Author: centosinfra-prod-github-app[bot]

fedora-ci/configuration.md

@@ -6,5 +6,9 @@ sidebar_position: 3
 During the development phase, maintainers can opt in by adding their dist-git repository to the configuration [here](https://github.com/packit/deployment/blob/2cd9e846a6ab1c320f6a6c589e4bcab6b3cfb762/secrets/packit/prod/packit-service.yaml.j2#L105)
 and submitting a [pull request](https://github.com/packit/deployment/pulls).
 
+You can use [scripts/enroll-users.py](https://github.com/packit/deployment/blob/main/scripts/enroll-users.py)
+to enroll all packages maintained by you or your group (similar to the now obsolete [zuul-config-generator](https://github.com/befeleme/zuul-config-generator)).
+Simply create a new branch, run the script as `./scripts/enroll-useres.py <fas-username>` and commit the changes.
+
 In later phases, CI will run by default on all packages. The exact details of test plan configuration are still
 being finalized, but the plan is to have a global default configuration that works well for most repositories.