Improve definitions of CI and CD in Episode 1
See these comments:
- https://gitlab.hzdr.de/hifis/software/education/gitlab-ci/workshop-materials/-/merge_requests/2#note_1391874
- https://gitlab.hzdr.de/hifis/software/education/gitlab-ci/workshop-materials/-/merge_requests/2#note_1391875
- https://gitlab.hzdr.de/hifis/software/education/gitlab-ci/workshop-materials/-/merge_requests/2#note_1393383
- https://gitlab.hzdr.de/hifis/software/education/gitlab-ci/workshop-materials/-/merge_requests/2#note_1393384
- https://gitlab.hzdr.de/hifis/software/education/gitlab-ci/workshop-materials/-/merge_requests/2#note_1393385