chore: update TODO.md

[skip]

TODO.md

@@ -3,11 +3,13 @@
 ## Global
 
 - [x] use `thiserror` in the library
-- [ ] cleanup error types, for instance `UnexpectedOutput`
+- [x] cleanup error types, for instance `UnexpectedOutput`
 - [ ] go over functions such as windows_related_to which return copies, and make
   them return references instead
 - [x] check clap config file support
 - [ ] use the strategy option only in save and catalog commands
+- [ ] use the `dirs` crate for XDG-related directories
+- [ ] use `config-rs` crate for the upcoming config file
 
 ## Related to save
 
@@ -17,7 +19,6 @@
 
 - [x] if in $TMUX, replace the existing session named `0` and switch to client
   else display a message `tmux attach -t last-session-name`
-- [ ] add `restore --attach` to automatically attach if running from the terminal
 - [ ] add `restore --override` to replace each existing session by its version from
   the archive
 - [ ] add `restore --skip-last-lines n` to not restore the last n lines of each