add repo and country info for singapore

added singapore nodeschool country code and repository link to `singapore.json`
So @finnp @sayanee when `location` is a country, then on the chapters page it shows up as "[ Singapore, SG ]" which isn't a huge deal but doesn't really make sense. That's why I left the country off that file so that it just says "[ Singapore ]" on the chapters page.

That's kind of a confusing way to do things, so I'm open to better suggestions!