[PATCH] docs: Better mention of qemu-img amend limitations

[Eric Blake]

Missed during merge resolution of commit bc5ee6da71.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 docs/tools/qemu-img.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/docs/tools/qemu-img.rst b/docs/tools/qemu-img.rst
index c35bd6482203..2b5891b54db7 100644
--- a/docs/tools/qemu-img.rst
+++ b/docs/tools/qemu-img.rst
@@ -265,6 +265,10 @@ Command description:
   --force allows some unsafe operations. Currently for -f luks, it allows to
   erase the last encryption key, and to overwrite an active encryption key.

+  The set of options that can be amended are dependent on the image
+  format, but note that amending the backing chain relationship should
+  instead be performed with ``qemu-img rebase``.
+
 .. option:: bench [-c COUNT] [-d DEPTH] [-f FMT] 
[--flush-interval=FLUSH_INTERVAL] [-i AIO] [-n] [--no-drain] [-o OFFSET] 
[--pattern=PATTERN] [-q] [-s BUFFER_SIZE] [-S STEP_SIZE] [-t CACHE] [-w] [-U] 
FILENAME

   Run a simple sequential I/O benchmark on the specified image. If ``-w`` is
-- 
2.28.0