prettier#15970: add change log file

changelog_unreleased/markdown/16231.md

@@ -0,0 +1,29 @@
+#### Markdown: format correctly table when columns are missing (#16231 by @yanapeycheva)
+
+<!-- prettier-ignore -->
+```md
+<!-- Input -->
+a | b
+:-- | :-- | :--
+a | b | c
+a || c
+a | b
+a |
+
+<!-- Prettier stable -->
+| a   | b   |     |
+| :-- | :-- | :-- |
+| a   | b   | c   |
+| a   |     | c   |
+| a   | b   |     |
+| a   |     |     |
+
+<!-- Prettier main -->
+| a   | b   |
+| :-- | :-- | :-- |
+| a   | b   | c   |
+| a   |     | c   |
+| a   | b   |
+| a   |
+
+```