mark done in README

README.md

@@ -64,9 +64,9 @@ This is my implementation of a note-taking app, organized around the following p
 - [x] persistence
 - [x] nice design
 - [x] navigation by link
-- [ ] sidebar improvements
-   - [ ] display and sort by last modified time
-   - [ ] show first couple rows of content
+- [x] sidebar improvements
+   - [x] display and sort by last modified time
+   - [x] show first couple rows of content
 - [ ] package to be deployed by Nix
 - [ ] the module layout reflects some old design ideas (`Node.Content`, `Node` being separate from `Database.Row`)
 - [ ] too many things are named `Node`. There's `Node`, `Node.Content.Node`, and I think a few others