Add support for Mechanic

I've added in the repository key to your `info.plist`, in order to make SidebearingsEQ updatable through Mechanic. In order for someone to start fetching updates, you'll have to tag the current release with your current version number (1.2). You can check out the Developer section on the Mechanic repository for the appropriate git commands.

If you accept this pull request, and if you like, I'll add SidebearingsEQ to Mechanic's project registry so that it can be installed through Mechanic's interface.