docs: clarify codex resume --all (CWD column & filtering) (#8264)

This pull request makes a small update to the session picker
documentation for `codex resume`. The main change clarifies how to view
the original working directory (CWD) for sessions and when the Git
branch is shown.

- The session picker now displays the recorded Git branch when
available, and instructions are added for showing the original working
directory by using the `--all` flag, which also disables CWD filtering
and adds a `CWD` column.