qemu-doc: Add the paragraph about the -no-frame deprecation again

The section has accidentially been removed while resolving a
contextual conflict during a rebase, so add this again.

Fixes: f29d4450
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <1520405769-22179-1-git-send-email-thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

qemu-doc.texi

@@ -2732,6 +2732,12 @@ filesystem test suite. Also it requires the CAP_DAC_READ_SEARCH capability,
 which is not the recommended way to run QEMU. This backend should not be
 used and it will be removed with no replacement.
 
+@subsection -no-frame (since 2.12.0)
+
+The @code{--no-frame} argument works with SDL 1.2 only. The other user
+interfaces never implemented this in the first place. So this will be
+removed together with SDL 1.2 support.
+
 @subsection -rtc-td-hack (since 2.12.0)
 
 The @code{-rtc-td-hack} option has been replaced by