docs: fix build-iso example (#2026)

add the "--bootloader-in-rootfs" flag

Signed-off-by: Francesco Giudici <[email protected]>

Author: fgiudici

docs/content/en/docs/Creating derivatives/build_iso.md

@@ -12,7 +12,7 @@ In order to build an ISO we rely on `elemental build-iso` command. It accepts a
 To build an ISO, just run:
 
 ```bash
-docker run --rm -ti -v $(pwd):/build ghcr.io/rancher/elemental-toolkit/elemental-cli:latest --debug build-iso -o /build $SOURCE
+docker run --rm -ti -v $(pwd):/build ghcr.io/rancher/elemental-toolkit/elemental-cli:latest --debug build-iso --bootloader-in-rootfs -o /build $SOURCE
 ```
 
 Where `$SOURCE` might be the container image you want to build the ISO for, you might want to check on [how to build bootable images](../creating_bootable_images). Argument `$SOURCE` might be the reference to the directory, file, container image or channel we are building the ISO for, it should be provided as uri in following format <sourceType>:<sourceName>, where: