Be a bit more explicit what kind of suggestions are are interested.

README

@@ -32,8 +32,12 @@ Copyright 2006-2016 Frans Kaashoek, Robert Morris, and Russ Cox.
 
 ERROR REPORTS
 
-If you spot errors or have suggestions for improvement, please send
-email to Frans Kaashoek and Robert Morris (kaashoek,rtm@csail.mit.edu).
+If you spot errors or have suggestions for improvement, please send email to
+Frans Kaashoek and Robert Morris (kaashoek,rtm@csail.mit.edu).  If you have
+suggestions for improvements, please keep in mind that the main purpose of xv6
+is as a teaching operating systems for MIT's 6.828. For example, we are in
+particular interested in reducing code, instead of suggestions for new systems
+calls, more portability, etc.
 
 BUILDING AND RUNNING XV6