Name plainMarkdownToAdf in the empty-markdown changelog entry

CHANGELOG.md

@@ -8,8 +8,8 @@
   fence whose info string `adf:<type>` names the node's type, its body the node's JSON without
   `type`: text holding an unescaped `!adf:` and a code fence whose info string opens `adf:` are
   claimed, and `adf` is an ordinary code block language. Convert stored markdown per `MIGRATION.md`.
-- **Breaking:** `markdownToAdf` reads markdown holding no block as a document whose `content` is
-  empty, as Atlassian's schema requires; `!adf:doc {content=none}` spells a document holding no
+- **Breaking:** `markdownToAdf` and `plainMarkdownToAdf` read markdown holding no block as a
+  document whose `content` is empty, as Atlassian's schema requires; `!adf:doc {content=none}` spells a document holding no
   `content` key.
 - `markdownToAdf(adfToMarkdown(doc))` deep-equals `doc`: two adjacent text nodes a reader would
   join are parted by `!adf:textBreak{}`, an empty `attrs`, `content` or `marks` is spelled