Editorial: disambiguate with statement's status (#2441)

Co-authored-by: Daniel D. Beck <daniel@ddbeck.com>
Co-authored-by: Michael Ficarra <mficarra@shapesecurity.com>

spec.html

@@ -21933,8 +21933,12 @@ <h1>Runtime Semantics: Evaluation</h1>
     </emu-clause>
   </emu-clause>
 
-  <emu-clause id="sec-with-statement">
+  <emu-clause id="sec-with-statement" legacy>
     <h1>The `with` Statement</h1>
+    <emu-note>
+      <p>Use of the Legacy `with` statement is discouraged in new ECMAScript code. Consider alternatives that are permitted in both strict mode code and non-strict code, such as <emu-xref href="#sec-destructuring-assignment">destructuring assignment</emu-xref>.</p>
+    </emu-note>
+
     <h2>Syntax</h2>
     <emu-grammar type="definition">
       WithStatement[Yield, Await, Return] :