Rename ci yaml readme to index

app/views/projects/pipelines/_with_tabs.html.haml

doc/administration/instance_limits.md

doc/administration/job_artifacts.md

doc/api/commits.md

doc/api/job_artifacts.md

doc/api/lint.md

doc/api/templates/gitlab_ci_ymls.md

doc/ci/caching/index.md

doc/ci/chatops/index.md

doc/ci/cloud_deployment/index.md

doc/ci/directed_acyclic_graph/index.md

doc/ci/docker/using_docker_build.md

doc/ci/docker/using_docker_images.md

doc/ci/enable_or_disable_ci.md

doc/ci/environments/deployment_safety.md

doc/ci/environments/index.md

doc/ci/examples/end_to_end_testing_webdriverio/index.md

doc/ci/examples/laravel_with_gitlab_and_envoy/index.md

doc/ci/index.md

doc/ci/jobs/index.md