doc/instances: clarify how to override device options during creation

Signed-off-by: Ruth Fuchss <[email protected]>

doc/howto/instances_backup.md

@@ -284,6 +284,8 @@ To import an export file, use the following command:
 If you do not specify an instance name, the original name of the exported instance is used for the new instance.
 If an instance with that name already (or still) exists in the specified storage pool, the command returns an error.
 In that case, either delete the existing instance before importing the backup or specify a different instance name for the import.
+
+Add the `--storage` flag to specify which storage pool to use, or the `--device` flag to override the device configuration (syntax: `--device <device_name>,<device_option>=<value>`).
 ```
 ```{group-tab} API
 To import an export file, post it to the `/1.0/instances` endpoint:

doc/howto/instances_create.md

@@ -27,7 +27,7 @@ See [`lxc launch --help`](lxc_launch.md) or [`lxc init --help`](lxc_init.md) for
 The most common flags are:
 
 - `--config` to specify a configuration option for the new instance
-- `--device` to override {ref}`device options <devices>` for a device provided through a profile, or to specify an {ref}`initial configuration for the root disk device <devices-disk-initial-config>`
+- `--device` to override {ref}`device options <devices>` for a device provided through a profile, or to specify an {ref}`initial configuration for the root disk device <devices-disk-initial-config>` (syntax: `--device <device_name>,<device_option>=<value>`)
 - `--profile` to specify a {ref}`profile <profiles>` to use for the new instance
 - `--network` or `--storage` to make the new instance use a specific network or storage pool
 - `--target` to create the instance on a specific cluster member