Update implementation notes for the arm64-linux port.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13775 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/Makefile.am b/Makefile.am
index 28087d9..40e2b0f 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -104,6 +104,7 @@
 	README.android \
 	README.android_emulator \
 	README.mips \
+	README.aarch64 \
 	NEWS.old \
 	valgrind.pc.in \
 	valgrind.spec.in \