docs: add missing docs for "DOCKER_TLS" env-var

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

docs/reference/commandline/cli.md

@@ -134,6 +134,7 @@ line:
 | `DOCKER_DEFAULT_PLATFORM`     | Default platform for commands that take the `--platform` flag.                                                                                                                                                                                               |
 | `DOCKER_HIDE_LEGACY_COMMANDS` | When set, Docker hides "legacy" top-level commands (such as `docker rm`, and `docker pull`) in `docker help` output, and only `Management commands` per object-type (e.g., `docker container`) are printed. This may become the default in a future release. |
 | `DOCKER_HOST`                 | Daemon socket to connect to.                                                                                                                                                                                                                                 |
+| `DOCKER_TLS`                  | Enable TLS for connections made by the `docker` CLI (equivalent of the `--tls` command-line option). Set to a non-empty value to enable TLS. Note that TLS is enabled automatically if any of the other TLS options are set.                                 |
 | `DOCKER_TLS_VERIFY`           | When set Docker uses TLS and verifies the remote. This variable is used both by the `docker` CLI and the [`dockerd` daemon](dockerd.md)                                                                                                                      |
 | `BUILDKIT_PROGRESS`           | Set type of progress output (`auto`, `plain`, `tty`) when [building](build.md) with [BuildKit backend](https://docs.docker.com/build/buildkit/). Use plain to show container output (default `auto`).                                                        |