[docs-scanner] Daemon configuration overview incomplete - missing environment variables method

[docker-agent]

File: content/manuals/engine/daemon/_index.md

Issue

The daemon configuration overview states there are only two ways to configure the Docker daemon, but omits environment variables as a third configuration method:

There are two ways to configure the Docker daemon:

• Use a JSON configuration file. This is the preferred option, since it keeps
  all configurations in a single place.
• Use flags when starting dockerd.

However, proxy.md in the same directory documents environment variables as a distinct configuration method:

There are two ways you can configure these settings:

• Configuring the daemon through a configuration file or CLI flags
• Setting environment variables on the system

Why this matters

A reader following the overview page would not learn about environment variables as a configuration option. When they later encounter proxy configuration documentation that relies on environment variables, they may be confused about whether this is a general daemon configuration method or specific to proxies only.

The overview page should provide a complete picture of all daemon configuration methods so readers understand their options from the start.

Suggested fix

Update the "Configure the Docker daemon" section in _index.md to mention all three configuration methods:

There are three ways to configure the Docker daemon:

- Use a JSON configuration file. This is the preferred option, since it keeps
  all configurations in a single place.
- Use flags when starting `dockerd`.
- Set environment variables in the daemon's startup environment (used for specific settings like proxy configuration).

Or add a note that some specific configurations (like proxies) can also use environment variables, with a link to the relevant documentation.

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Found by nightly documentation quality scanner