docs: make GHA default, docker optional

See e.g. https://partner.github.com/integration-resources/2020/11/24/pattern-setting-up-a-cli-on-github-s-hosted-runners.html

Would make it super easy to set up:

jobs:
  run:
    runs-on: [ubuntu-latest]
    steps:
      - uses: actions/checkout@v2
      - uses: iterative/cml@v1
      - name: 'Train my model'
        ...
        cml-send-comment report.md

EDIT:

- uses: actions/setup-node@v1
- uses: iterative/setup-cml@v1

works well but needs better documentation. Any objections to making it more prominent than container: docker://? Would fix e.g. #360

[DavidGOrtega]

@casperdcl @0x2b3bfa0 actions/setup-node@v1 might not be needed at all since its de facto in GHA.

I encourage using docker of course but not our image in GHA but the user’s. Thats why we changed CML a bit. Our cml.dev examples pushes the user to use the action instead our container but seems that we forgot this here?

I wont think that this fix #360 unfortunately since we have to support Gitlab and that job (better tagging) has to be done anyway.

[casperdcl]

Well actions/setup-node@v1 is needed if you want to pin the version or often needed in self-hosted but I’m sure you knew that. Will certainly point it out in the docs…

I think the usual point of container: docker:// is for end-users to define their own containers. CML’s containers are to me more of a proof-of-concept than something we should be actively recommending people use.