docs: import: update documentation for --platform

The `--platform` flag originally was added for the experimental LCOW
feature and only accepted the target operating system. Current versions
of Docker allow passing both OS and Architecture, so updating the
documentation to reflect this.

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

Author: thaJeztah

docs/reference/commandline/image_import.md

@@ -13,7 +13,7 @@ Import the contents from a tarball to create a filesystem image
 |:------------------------------------------|:---------|:--------|:--------------------------------------------------|
 | [`-c`](#change), [`--change`](#change)    | `list`   |         | Apply Dockerfile instruction to the created image |
 | [`-m`](#message), [`--message`](#message) | `string` |         | Set commit message for imported image             |
-| `--platform`                              | `string` |         | Set platform if server is multi-platform capable  |
+| [`--platform`](#platform)                 | `string` |         | Set platform if server is multi-platform capable  |
 
 
 <!---MARKER_GEN_END-->
@@ -120,3 +120,31 @@ daemon.
 ```console
 $ docker import --platform=linux .\linuximage.tar
 ```
+
+### <a name="platform"></a> Set the platform for the imported image (--platform)
+
+The `--platform` option allows you to specify the platform for the imported
+image. By default, the daemon's native platform is used as platform, but
+the `--platform` option allows you to override the default, for example, in
+situations where the imported root filesystem is for a different architecture
+or operating system.
+
+The platform option takes the `os[/arch[/variant]]` format; for example,
+`linux/amd64` or `linux/arm64/v8`. Architecture and variant are optional,
+and default to the daemon's native architecture if omitted.
+
+The following example imports an image from a root-filesystem in `rootfs.tgz`,
+and sets the image's platform to `linux/amd64`;
+
+```console
+$ docker image import --platform=linux/amd64  ./rootfs.tgz imported:latest
+sha256:44a8b44157dad5edcff85f0c93a3e455f3b20a046d025af4ec50ed990d7ebc09
+```
+
+After importing the image, the image's platform is set in the image's
+configuration;
+
+```console
+$ docker image inspect --format '{{.Os}}/{{.Architecture}}' imported:latest
+linux/amd64
+```