doc: add changelogs for punycode

PR-URL: #11489
Reviewed-By: Ben Noordhuis <[email protected]>
Reviewed-By: Sam Roberts <[email protected]>
Reviewed-By: Roman Reiss <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Italo A. Casas <[email protected]>

Author: addaleax

doc/api/punycode.md

@@ -1,4 +1,10 @@
 # Punycode
+<!-- YAML
+changes:
+  - version: v7.0.0
+    pr-url: https://github.com/nodejs/node/pull/7941
+    description: Accessing this module will now emit a deprecation warning.
+-->
 
 > Stability: 0 - Deprecated