Refactor autoscale doc
Refactor autoscale doc

- Add TOC
- Reorganize sections
- Add more examples

[ci skip]

soiff/gitlab-ci-multi-runner,hu19891110/gitlab-ci-multi-runner,ayufan/gitlab-ci-multi-runner,ayufan/gitlab-ci-multi-runner,soiff/gitlab-ci-multi-runner,hu19891110/gitlab-ci-multi-runner,ayufan/gitlab-ci-multi-runner,soiff/gitlab-ci-multi-runner,hu19891110/gitlab-ci-multi-runner