Improvements and Clarifications for GitLab CI/CD Documentation

[refoo0]

By using GitLab CI/CD documentation:

• The pictures are small; maybe we could add an option to click on the picture to expand it.
• If the text in fields is too wide, you can't see it, and there's no option to scroll horizontally.
• I find the instruction "1. Open the CI/CD project settings in GitLab" a bit confusing for people who are not familiar with GitLab. Maybe it would be clearer to write: GitLab -> Project -> Settings -> CI/CD
• In the step "Create or insert the YAML snippet inside a .github/workflows file", it should be changed to "Create or insert the YAML snippet inside a .gitlab-ci.yml file".
• The step to set up webhooks in GitLab is missing.