Move note about different backends and features to top

README.md

@@ -13,7 +13,8 @@ that would normally come with a full Perl 6 distribution.  If you're
 after more than just the bare compiler, please download [the latest
 Rakudo Star package](http://rakudo.org/downloads/star).
 
-For a high-level overview of implemented and missing features,
+Note that different backends implement slightly different sets of
+featurs. For a high-level overview of implemented and missing features,
 please visit <http://perl6.org/compilers/features>.
 
 ## Building and Installing Rakudo
@@ -47,9 +48,6 @@ download an build a fresh NQP, run:
 
     perl Configure.pl --gen-nqp --backends=jvm
 
-Note that Rakudo on JVM implements a slightly different set of features
-than Rakudo on Parrot.
-
 If you get an out of memory error building rakudo on the JVM, you may
 need to modify your NQP runner to limit memory use. e.g. Adding
 `-Xms500m -Xmx2g` as options passed to java in the installed nqp / nqp.bat.