Add .DS_Store to gitignore

[philsmart]

Should be quick. So I will merge once I've spoken quickly to @iay back-channel.

[iay]

Fine to merge.

I would mention, however, that a cautious developer might consider using the ~/.gitignore_global file to hold the names of random garbage that their local system has a tendency to generate. If you're not using that already (as a backstop) it's worth doing; you need to set it up in your ~/.gitconfig.

[philsmart]

Ah, thanks. I do have that in ~/.gitignore_global so I guess it must not be setup correctly in ~/.gitconfig. I'll do that now.

[iay]

Mine has

[core]
        editor = code --wait --new-window
        excludesfile = ~/.gitignore_global

[philsmart]

Thanks. I was missing the core section and excludesfile.