Minor NetBSD/DragonFly/pkgsrc build instruction update

Add -I/usr/pkg/include to NetBSD/Dragon Fly build example CPPFLAGS.
This is needed to pick up libftdi.

Corresponding to flashrom svn r1519.

Signed-off-by: Jonathan A. Kollasch <jakllsch@kollasch.net>
Acked-by: Uwe Hermann <uwe@hermann-uwe.de>
diff --git a/README b/README
index a94cae8..f88b3b5 100644
--- a/README
+++ b/README
@@ -83,7 +83,8 @@
 To compile on NetBSD or DragonFly BSD, use:
 
  ln -s /usr/pkg/include/pciutils pci
- gmake CPPFLAGS=-I. LDFLAGS="-L/usr/pkg/lib -Wl,-rpath-link,/usr/pkg/lib"
+ gmake CPPFLAGS="-I. -I/usr/pkg/include" \
+       LDFLAGS="-L/usr/pkg/lib -Wl,-rpath-link,/usr/pkg/lib"
 
 To compile on OpenBSD, use: