Fix install instructions

[fhoekstra]

As per the discussion and solutions provided around here: https://github.com/dracula/zsh/issues/11#issuecomment-1429361016

The instructions for manual install and git install as they are on https://draculatheme.com/zsh right now don't work for me and other users. This git install method works and is confirmed by multiple users. The instructions for the non-git install should have the same result, except for the missing .git folder.

If you're fixing a UI issue, make sure you take two screenshots. One that shows the actual bug and another that shows how you fixed it.