modify mac-dev-playbook to be used for ansible-pull

[ta-yuhyeon]

Hi all,

just a consideration, as the repository is public, isn't it better to make this repo usable with ansible-pull?
adding a local.yml instead of main.yml then proceding to run
ansible-pull --url https://github.com/geerlingguy/mac-dev-playbook.git

ofc the prerequisites must be to have xcode and ansible but it will probably make the overall installation more fluid specially if you are trying to run it in a brand new mac or macbook.