Add subcommand that converts existing repository

Close #6

src/cmd.rs

@@ -83,6 +83,8 @@ pub enum WorktreeAction {
     Delete(WorktreeDeleteArgs),
     #[clap(about = "Show state of existing worktrees")]
     Status(WorktreeStatusArgs),
+    #[clap(about = "Convert a normal repository to a worktree setup")]
+    Convert(WorktreeConvertArgs),
     #[clap(about = "Clean all worktrees that do not contain uncommited/unpushed changes")]
     Clean(WorktreeCleanArgs),
 }
@@ -116,6 +118,9 @@ pub struct WorktreeDeleteArgs {
 #[derive(Parser)]
 pub struct WorktreeStatusArgs {}
 
+#[derive(Parser)]
+pub struct WorktreeConvertArgs {}
+
 #[derive(Parser)]
 pub struct WorktreeCleanArgs {}