docs: document comparing docs.json changes in the editor

editor/review.mdx

@@ -122,14 +122,14 @@
 
 When your project requires review before publishing, branches you create in the editor use the same review flow as your deployment branch. You request reviews and approve changes in the editor, and you don't see the branch's pull request. When you publish, the editor merges the branch into your deployment branch.
 
 A review on a branch covers the whole branch. Every page of the branch shows one banner, such as **This branch is under review by** followed by the reviewers' names, and then **This branch is approved.** Clicking **Approve** in the banner approves the branch in one step.
 
 - A branch publishes all at once. An admin or publisher can publish it only after reviewers approve every change on the branch. Then they click **Publish approved changes**.
 - Changes to navigation, site settings, and other files that aren't pages go into the review as **Site changes**. Until a reviewer approves them, only an admin can publish the branch.
 - Admins can publish a branch at any time.
 - Anyone who can approve changes can approve a branch, except the person who created the branch and the person who requested the review.
 - If you move or reorder an approved page, only that page needs another review. Adding a page or changing navigation doesn't affect the approvals on other pages.
 - If you edit the branch after approval, or someone pushes a change to it in Git, the banner shows **You edited this branch after it was approved** or **This branch changed in git after it was approved**. Click **Request review again** to ask the reviewers to review it again.
 - Pages you delete on the branch are part of the review too. They appear as **Removed**, and reviewers approve them like any other page. A removed page's link in the review banner opens the page on your deployment branch in a new tab.
 - If the branch no longer changes a requested page, the page leaves the review request.
 - Reviews that teammates leave on the branch's pull request in GitHub appear in the review request and in the [inbox](/dashboard/inbox) for reference. They don't count as approvals in the editor.
@@ -176,7 +176,9 @@
 
 Click any changed file in the publish menu to open it in diff view against the published version. To leave diff view, click **Viewing changes** in the top bar. Visual mode shows a visual diff and source mode shows a text diff. Files that can't display a diff, such as images or deleted files, appear in the list but aren't clickable.
 
-In a source mode diff of a page, choose **Unified** or **Split** in the top bar to show changes in one column or side by side. Until you choose, the editor picks the layout that fits your window width. The editor remembers your choice for later diffs.
+To compare `docs.json` with the version on the branch your changes publish to, open `docs.json` in source mode and click **Show changes** in the top bar. The editor shows a read-only text diff. Click **Hide changes** to go back to editing.
+
+In a source mode diff of a page or `docs.json`, choose **Unified** or **Split** in the top bar to show changes in one column or side by side. Until you choose, the editor picks the layout that fits your window width. The editor remembers your choice for later diffs.
 
 You can open [hidden pages](/organize/hidden-pages) that appear in the branch diff from the publish menu, even though they don't appear in your site navigation.