fix the git pull issue

[Utkar5hM]

Finally fixed it with codex.

• git pull with no arguments usually uses the configured remote, typically origin, plus its fetch refspec. That often updates origin/* remote-tracking refs, so Git learns about new branches.
• git pull pulls from an arbitrary URL into FETCH_HEAD and updates the current checked-out branch. It does not guarantee a local branch named <branch_name>, and it may not create origin/<branch_name> either.
• git checkout <branch_name> is a separate step. It only works if that branch already exists locally, or Git can see a matching remote-tracking branch.

solves #9.