[Doc] Add sample/starter appveyor (+ other CI) configuration docs

I know, I know, I should have had my project on CI from day 1, but for non-FOSS it costs money and there were politics to deal with (insert more lame excuses here). However, I am just now getting my ember-electron project setup on AppVeyor, and I'm sure I am re-inventing the wheel a bit. The docs here don't seem to talk much about setting up CI for ember-electron projects (arguably, it's not that hard & is out of scope), but I think it would be helpful to have a doc in the FAQ section that includes a collection of sample configuration files for various CI systems like AppVeyor, Circle, and Travis.

**Would anyone out there be willing to share their configuration / notes here?** If so, I'll gladly organize them into a doc and create a PR. I suspect that people will be especially interested in gotchas regarding code-signing & packaging for Mac & Microsoft app stores.