Ad md timeline note

release-notes/v1_65.md

@@ -540,6 +540,10 @@ Every milestone comes with new proposed APIs and extension authors can try them
 
 You cannot publish an extension that uses a proposed API. There may be breaking changes in the next release and we never want to break existing extensions.
 
+### Markdown Hovers in Timeline Items
+
+Item provided with a `TimelineProvider` now support markdown in the `detail` property, used to provide content for their tooltip.
+
 ### Notebook aware document selectors
 
 The `vscode.DocumentSelector` type allows you to associate language features like **Go to Definition** to specific documents. This drives the UI and also decides if the corresponding provider is asked for results. We have added a new API proposal that allows to also select notebook types, like `{ language: 'python', notebookType: 'jupyter-notebook'}` targets all python documents that are embedded in Jupyter notebooks. This is the [current proposal](https://github.com/microsoft/vscode/blob/8a3b1f4c4c24064273efb3417a5c2e229ba78481/src/vscode-dts/vscode.proposed.notebookDocumentSelector.d.ts) - give it a try and let us know what you think.