feat: `list` subcommand

[notnmeyer]

adds a list subcommand to print an ugly tree view of a project,

✦ ➜ go run main.go list
 default/
   2023/
     09/
       29/
         log.md
     10/
       02/
         log.md
       13/
         log.md
     11/
       03/
         log.md
       09/
         log.md
       10/
         log.md
       11/
         log.md
       13/
         log.md
       21/
         log.md

useful for when you want to look back at a previous day but youre not sure what the date was