cli reference overview base cmd

[dvdksn]

- What I did

Moves the cli.md file to become the docker.md base command reference.

This file contains a lot of information about how the CLI and its flags work, base flags, configuration file, and environment variables. I think it makes more sense to have it on the base command page than in a separate place.

Needs:

• fix: generate long desc and examples for root command cli-docs-tool#53

- How I did it

- How to verify it

- Description for the changelog

- A picture of a cute animal (not mandatory but encouraged)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 61.48%. Comparing base (1dee86b) to head (dc22572).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5010   +/-   ##
=======================================
  Coverage   61.48%   61.48%           
=======================================
  Files         298      298           
  Lines       20814    20814           
=======================================
  Hits        12797    12797           
  Misses       7105     7105           
  Partials      912      912           

[thaJeztah]

LGTM, thanks!

[thaJeztah]

Not for this PR, but we need to look at some of these; -a / --attach is shown as list, and those can take multiple values, but for other flags, Cobra is good at silently ignoring duplicates, and in that case overriding previous values. (e.g. -i -i=false -i=true -i)

Also for a follow-up, we should pick a different example than -a, as it's really more of an "expert" use-case to set that. Perhaps something like -e / --env or something common could be a good one to pick as example (the --env one can be nice as we could show the result;

$ docker run --rm -e ENV_ONE=one -e ENV_TWO=two alpine printenv
ENV_ONE=one
ENV_TWO=two
<...>
```.