Document new command-line interface structure

[0x2b3bfa0]

The following pull request have introduced some drastic naming changes that should be documented:

• Integrate cml publish with cml send-comment cml#1026
• Introduce subcommands in a backwards-compatible way cml#1073

Note
Closing this issue won't only require updating the documentation, but also all the active example repositories and material.

• https://cml.dev/ document new subcommands #324
  • https://cml.dev/doc/
    • https://cml.dev/doc/ref/
      • runner
      • comment
      • check
      • pr
      • workflow
      • tensorboard
    • DVCLive demo for --watch --publish guide: DVCLive reports #327
• cml readme
• example repos https://github.com/iterative/cml-examples-dev/issues/9
  • GH
  • GL
  • BB
• https://github.com/iterative/cml/labels

[jorgeorpinel]

Removing labels that #324 seems to have taken care of.

I'd consider transferring this to cml if the main thing missing is the REAMDE update.
p.s. but iterative/cml#718 ?