[Trivial] docs: More precisely describe memory-backend-*::id's user

[Robert Hoo]

'id' of memory-backend-{file,ram} is not only for '-numa''s reference, but
also other parameters like '-device nvdimm'.
More clearly call out this to avoid misinterpretation.

Signed-off-by: Robert Hoo <robert.hu@linux.intel.com>
---
 qemu-options.hx | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/qemu-options.hx b/qemu-options.hx
index fd21002..635dc8a 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4508,11 +4508,11 @@ SRST
         the guest RAM with huge pages.
 
         The ``id`` parameter is a unique ID that will be used to
-        reference this memory region when configuring the ``-numa``
-        argument.
+        reference this memory region in other parameters, e.g. ``-numa``,
+        ``-device nvdimm``, etc.
 
         The ``size`` option provides the size of the memory region, and
-        accepts common suffixes, eg ``500M``.
+        accepts common suffixes, e.g. ``500M``.
 
         The ``mem-path`` provides the path to either a shared memory or
         huge page filesystem mount.
-- 
1.8.3.1