Setting up worktree with git doesn't seem to work

**Issue**
When following the README, the setup of the worktree with the command `git worktree add -b 4.0 var/versions/4.0` doesn't seem to work.
Viewing the site gives a 404 error, saying var/versions/4.0/docs does not exist. The folder is indeed not present.
Running the command didn't give any errors or feedback.

**Fast solution**
Setting up the worktree with the sed and grep method _does_ work.

**info**
php: 7.3.4
git version 2.11.0