Amend setup hints in README

Author: JoshuaBehrens

README.MacOS.md

@@ -16,7 +16,7 @@ cd /tmp
 git clone https://github.com/phpv8/v8js.git
 cd v8js
 phpize
-./configure --with-v8js=/opt/homebrew CPPFLAGS="-DV8_COMPRESS_POINTERS"
+./configure --with-v8js=/opt/homebrew CPPFLAGS="-DV8_COMPRESS_POINTERS -DV8_ENABLE_SANDBOX"
 make -j4
 make test
 make install