bootctl: add --root and --image

Operate on image/directory, and also take files to install from it

shell-completion/bash/bootctl

@@ -32,7 +32,7 @@ _bootctl() {
     local cur=${COMP_WORDS[COMP_CWORD]} prev=${COMP_WORDS[COMP_CWORD-1]}
     local -A OPTS=(
         [STANDALONE]='-h --help -p --print-esp-path -x --print-boot-path --version --no-variables --no-pager --graceful'
-        [ARG]='--esp-path --boot-path --make-machine-id-directory'
+        [ARG]='--esp-path --boot-path --make-machine-id-directory --root --image'
     )
 
     if __contains_word "$prev" ${OPTS[ARG]}; then
@@ -48,6 +48,10 @@ _bootctl() {
             --make-machine-id-directory)
                 comps="yes no auto"
                 ;;
+            --image|--root)
+                compopt -o nospace
+                comps=$( compgen -A file -- "$cur" )
+                ;;
         esac
         COMPREPLY=( $(compgen -W '$comps' -- "$cur") )
         return 0