Improve clarity of environment variables description

[ahopp]

Summary

Improved the clarity of the environment variables section description.

Changes

Changed the environment variables section description from:

The following list of environment variables are supported by the docker command line:

To:

The following environment variables control the behavior of the docker command-line client:

This change:

• Makes it clearer that these variables control Docker's behavior, not just that they are "supported"
• Uses the more precise term "command-line client" instead of "command line"
• Fixes the grammatical issue with "The following list...are supported" (subject-verb agreement)

Related Issue

https://github.com/docker/docs/pull/23620

Signed-off-by: Andrew Hopp [email protected]

[ahopp]

@dvdksn Fixing the issues mentioned in https://github.com/docker/docs/pull/23620 as requested.