Missing indentation.

A code example was missing 2 spaces on its indentation and Markdown was parsing it as regular text.
1799. Broken link for configuration reference.
Merge branch 'patch-1' of https://github.com/philgruneich/compass into philgruneich-patch-1
Adding an AppVeyor configuration file

AppVeyor is a Windows CI solution that provides a free service for open
source projects; this sets up for using ths service.