doc: add format-md step to release guide

PR-URL: #41809
Reviewed-By: Antoine du Hamel <[email protected]>
Reviewed-By: Richard Lau <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Tobias Nießen <[email protected]>
Reviewed-By: Mestery <[email protected]>
Reviewed-By: Darshan Sen <[email protected]>
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>

Author: danielleadams

doc/contributing/releases.md

@@ -312,6 +312,9 @@ of the list. The most recent release for each release line is shown in **bold**
 in the index. When updating the index, please make sure to update the display
 accordingly by removing the bold styling from the previous release.
 
+Run `make format-md` to ensure the `CHANGELOG_Vx.md` and `CHANGELOG.md` files
+are formatted correctly.
+
 #### Step 3: Update any REPLACEME and DEP00XX tags in the docs
 
 If this release includes new APIs then it is necessary to document that they