[PATCH] intro: add advice on transition from legacy interfaces

["Michael S. Tsirkin" <mst@redhat.com>]

Reading legacy chapters gives a hint about what changed,
let's help readers discover this useful shortcut.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 introduction.tex | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/introduction.tex b/introduction.tex
index ac7eefa..0c076f8 100644
--- a/introduction.tex
+++ b/introduction.tex
@@ -126,6 +126,16 @@ Similarly, a driver MAY implement:
 Devices or drivers with no legacy compatibility are referred to as
 non-transitional devices and drivers, respectively.
 
+\subsection{Transition from earlier specification drafts}
+\label{intro:Transition from earlier specification drafts}
+
+If a device or a driver already implement the legacy interface,
+some changes would have to be made to support this specification.
+
+In this case, it might be benefitial for the reader to focus on
+sections tagged "Legacy Interface" in the section title.
+These highlight the changes made since these earlier drafts.
+
 \section{Structure Specifications}
 
 Many device and driver in-memory structure layouts are documented using
-- 
MST