metadata/code: Mention dependency on core spec in the introduction

Author: yuri91

document/metadata/code/intro.rst

@@ -10,3 +10,9 @@ Such metadata do not contribute to, or otherwise affect, the WebAssembly semanti
 
 However, it can provides useful information that implementations can make use of to improve user experience or take compilation hints.
 
+Dependencies
+~~~~~~~~~~~~
+
+This document is based on the WebAssembly core specification (|WasmDraft|), and makes use of
+terms and definitions described there. These uses always link to the corresponding definition
+in the core specification.