Document possible values for `docker -H`

[agowa]

Problem description
docker -H supports multiple connections, but the documentation for it is either hard to find or non existent.

Problem location
I couldn't find the information I wanted. I expected to find it near the following URL: https://raw.githubusercontent.com/docker/docker-ce/master/components/cli/docs/reference/commandline/cli.md
Project version(s) affected
all

Suggestions for a fix
Mention that ssh://, tcp://, socket:// can be used to connect to dockerd.

(Reopen of #8303)

label:area/CLI
/lifecycle frozen

[dvdksn]

docker/cli#4260

[docker-robot]

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/lifecycle locked