bootutil; update signed_images.md with the new location of bootutil.
diff --git a/boot/bootutil/signed_images.md b/boot/bootutil/signed_images.md
index 64869c1..e7cc2dd 100644
--- a/boot/bootutil/signed_images.md
+++ b/boot/bootutil/signed_images.md
@@ -65,7 +65,7 @@
 
     pkg.name: libs/mykeys
     pkg.deps:
-        - libs/bootutil
+        - "@apache-mynewt-core/boot/bootutil"
 
 ## Sample source file
 This exports the keys.