Add _sass/cayman.scss to allow importing with theme name while using jekyll-remote-theme

Author: parkr

_sass/cayman.scss

@@ -0,0 +1,4 @@
+// Placeholder file. If your site uses
+//     @import "{{ site.theme }}";
+// Then using this theme with jekyll-remote-theme will work fine.
+@import "jekyll-theme-cayman";